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Recent research had claimed that an excess of positive ions (离子) in the air can have an ill-effect on people's physical or psychological health. What are positive ions? Well, the air is full of ions, electrically charged particles, and generally there is a rough balance between the positive and the negative charges. But sometimes this balance becomes disturbed and a larger proportion of positive ions are found. This happens naturally before thunderstorms, earthquakes or when winds are blowing in certain countries. Or it can be caused by a build-up of static electricity indoors from carpets or clothing made of man-made fibers, or from TV sets, duplicators or computer display screens.
When a large number of positive ions are present in the air many people experience unpleasant effects such as headaches, fatigue, irritability, and some particularly sensitive people suffer nausea (恶心) or even mental disturbance. Animals are also found to be affected, particularly before earthquakes; snakes have been observed to come out of hibernation(冬眠), rats to flee from their burrows, dogs howl and cats jump about unaccountably. This has led the US Geographical Survey to fund a network of volunteers to watch animals in all effort to foresee such disasters before they hit vulnerable areas such as California.
Conversely, when large numbers of negative ions are present, then people have a feeling of well-being. Natural conditions that produce these large amounts are near the sea, close to waterfalls or fountains, or in any place where water is sprayed, or forms a spray. This probably accounts for the beneficial effect of a holiday by the sea, or in the mountains with tumbling streams or waterfalls.
To increase the supply of negative ions indoors, some scientists recommend the use of ionizers : small portable machines which generate negative ions. They claim that ionizers not only clean and refresh the air but also improve the health of people sensitive to excess positive ions. Of course, there are the detractors, other scientists, who dismiss such claims and are skeptical about negative/positive ion research. Therefore people can only make up their own minds by observing the effects on themselves, or on others, of a negative rich or poor environment.
After all, it is debatable whether depending on seismic readings to anticipate earthquakes is more effective than watching the cat.
According to the passage, static electricity can be caused by
A．using home-made electrical goods.
B．wearing clothes made of natural materials.
C．walking on artificial floor coverings.
D．copying TV programs on a computer.
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更多 “ Recent research had claimed that an excess of positive ions (离子) in the air can have an ill-effect on people's physical or psychological health. What are positive ions? Well, the air is full of ions, electrically charged particles, and generally there is a rough balance between the positive and the negative charges. But sometimes this balance becomes disturbed and a larger proportion of positive ions are found. This happens naturally before thunderstorms, earthquakes or when winds are blowing in certain countries. Or it can be caused by a build-up of static electricity indoors from carpets or clothing made of man-made fibers, or from TV sets, duplicators or computer display screens.When a large number of positive ions are present in the air many people experience unpleasant effects such as headaches, fatigue, irritability, and some particularly sensitive people suffer nausea (恶心) or even mental disturbance. Animals are also found to be affected, particularly before earthquakes; snakes have been observed to come out of hibernation(冬眠), rats to flee from their burrows, dogs howl and cats jump about unaccountably. This has led the US Geographical Survey to fund a network of volunteers to watch animals in all effort to foresee such disasters before they hit vulnerable areas such as California.Conversely, when large numbers of negative ions are present, then people have a feeling of well-being. Natural conditions that produce these large amounts are near the sea, close to waterfalls or fountains, or in any place where water is sprayed, or forms a spray. This probably accounts for the beneficial effect of a holiday by the sea, or in the mountains with tumbling streams or waterfalls.To increase the supply of negative ions indoors, some scientists recommend the use of ionizers : small portable machines which generate negative ions. They claim that ionizers not only clean and refresh the air but also improve the health of people sensitive to excess positive ions. Of course, there are the detractors, other scientists, who dismiss such claims and are skeptical about negative/positive ion research. Therefore people can only make up their own minds by observing the effects on themselves, or on others, of a negative rich or poor environment.After all, it is debatable whether depending on seismic readings to anticipate earthquakes is more effective than watching the cat.According to the passage, static electricity can be caused byA．using home-made electrical goods.B．wearing clothes made of natural materials.C．walking on artificial floor coverings.D．copying TV programs on a computer. ” 相关考题
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What effect does excessive positive ions have on some people?A．They think they are mad.B．They feel very tired.C．They become violently sick.D．They are too tired to do anything.
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People should be able to come to a decision about ions in the air if theyA．note their own reactions.B．move to a healthier area.C．observe domestic animals.D．watch how wealthy people behave.
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Recent studies have shown that air inside many homes, office buildings, and schools is full of pollutants such as ().A、chemicalsB、smokeC、bacteriaD、perfume
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From what you _____, you can understand why an object weighs less in water than in air.A、had learntB、will learnC、have learntD、can learn
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Health implies more than physical fitness. It also implies mental and emotional well-being. An angry, frustrated, emotionally21 person in good physical condition is not 22healthy. Mental health, therefore, has much to do23 how a person copes with the world as s/he exists. Many of the factors that 24 physical health also affect mental and emotional well-being.Having a good self-image means that people have positive25 pictures and good, positive feelings about themselves, about what they are capable26, and about the roles they play. People with good self-images like themselves, and they are27 like others. Having a good self-image is based 28 a realistic, as well as positive, or optimistic29of one’s own worth and value and capabilities.Stress is an unavoidable, necessary, and potentially healthful 30 of our society. People of all ages 31 stress. Children begin to32stress during prenatal development and during childbirth. Examples of stress-inducing 33 in the life of a young person are death of a pet, pressure to 34 academically, the divorce of parents, or joining a new youth group. The different ways in which individuals35 to stress may bring healthful or unhealthy results. One person experiencing a great deal of stress may function exceptionally well 36 another may be unable to function at all. If stressful situations are continually encountered, the individual’s physical, social, and mental health are eventually affected.Satisfying social relations are vital to37 mental and emotional health. It is believed that in order to38, develop, and maintain effective and fulfilling social relationships people must 39 the ability to know and trust each other, understand each other, influence, and help each other. They must also be capable of40 conflicts in a constructive way.21.[A] unstable[B] unsure[C] imprecise[D] impractical
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第二篇As we have seen,the focus of medical care in our society has been shifting from curing disease to preventing disease一especially in terms of changing our many unhealthy behaviors,such as poor eating habits,smoking,and failure to exercise.The line of thought involved in this shift can be pursued further. Imagine a person who is about the right weight , but does not eat very nutritious（有营养的）foods , who feels OK but exercises only occasionally , who goes to work every day , but is not an outstanding worker,who drinks a few beers at home most nights but does not drive while drunk, and who has no chest pains or abnormal blood counts,but sleeps a lot and often feels tired.This person is not ill.He may not even be at risk for any particular disease.But we can imagine that this person could be a lot healthier.The field of medicine has not traditionally distinguished between someone who is merely "not ill" and someone who is in excellent health and pays attention to the body's special needs.Both types have simply been called "well".In recent years,however,some health specialists have begun to apply the terms "well" and "weilness" only to those who are actively striving to maintain and improve their body's condition.Most importantly,perhaps,people who are well take active responsibility for all matters related to their health.Even people who have a physical disease or handicap（缺陷）may be "well" ,in this new sense,if they make an effort to maintain the best possible health they can in the face of their physical limitations."Wellness" may perhaps best be viewed not as a state that people can achieve,but as an ideal that people can strive for. People who are well are likely to be better able to resist disease and to fight disease when it strikes.And by focusing attention on healthy ways of living,the concept of weilness can have a beneficial impact on the way in which people face the challenges of daily life.According to the second paragraph about the traditional care,which statement is true?A:if the person does not have' any unhealthy living habits,he is considered "well".B:If the person does not have any psychological disease,he is considererd "well".C:If the person could be able to handle his daily routines,he is considererd "well".D:If the nerson could be free from any kind of disease.he is considererd "well".
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Please Fasten Your SeatbeltsSevere turbulence（湍流）can kill aircraft passengers. Now,in test flights over the RockyMountains , NASA（美国航空航天局）engineers have successfully detected clear-air turbulence up to 10 seconds before an aircraft hits it.Clear-air turbulence often catches pilots by surprise.Invisible to radar,it is difficult to forecast and can hurl（用力抛出去）passengers about the cabin. In December 1 997 , one passenger died and a hundred others were injured when unexpected rough air caused a United Airlines flight over the Pacific to drop 300 meters in a few seconds.However,passengers can avoid serious injury by fastening their seatbelts.“It is the only antidote（对策）for this sort of thing,”says Rod Bogue,project manager at NASA's Dryden FlightResearch Center in Edwards,California.The centre's new turbulence detector is based on lidar,or laser radar. Laser pulses are sent ahead of the plane and these are then reflected back by particles in the air. The technique depends on the Doppler effect.The wavelength of the light shifts according to the speed at which the particles are approaching. In calm air,the speed equals the plane's airspeed.But as the particles swirl（打漩）in rough air,their speed of approach increases or decreases rapidly .The rate of change in speed corresponds to the severity（激烈程度）of the turbulence.In a series of tests that began last month,a research jet flew repeatedly into disturbed air over the mountain ridges（山脉）near Pueblo , Colorado. The lidar detector spotted turbulence between 3 and 8 kilometers ahead,and its forecasts of strength and duration corresponded closely with the turbulence that the plane encountered.Bogue says that he had“a comfortable amount of time”to fasten his seatbelt. The researchers are planning to improve the lidar's range with a more powerful beam.The system could be installed on commercial aircraft in the next few years.We can infer from the fifth paragraph that______.A: the lidar detector can successfully forecast turbulenceB: researchers are not sure about the effectiveness of the lidar detectorC: passenger planes will be used in further experimentsD: no more test flights are needed
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Please Fasten Your SeatbeltsSevere turbulence（湍流）can kill aircraft passengers. Now,in test flights over the RockyMountains , NASA（美国航空航天局）engineers have successfully detected clear-air turbulence up to 10 seconds before an aircraft hits it.Clear-air turbulence often catches pilots by surprise.Invisible to radar,it is difficult to forecast and can hurl（用力抛出去）passengers about the cabin. In December 1 997 , one passenger died and a hundred others were injured when unexpected rough air caused a United Airlines flight over the Pacific to drop 300 meters in a few seconds.However,passengers can avoid serious injury by fastening their seatbelts.“It is the only antidote（对策）for this sort of thing,”says Rod Bogue,project manager at NASA's Dryden FlightResearch Center in Edwards,California.The centre's new turbulence detector is based on lidar,or laser radar. Laser pulses are sent ahead of the plane and these are then reflected back by particles in the air. The technique depends on the Doppler effect.The wavelength of the light shifts according to the speed at which the particles are approaching. In calm air,the speed equals the plane's airspeed.But as the particles swirl（打漩）in rough air,their speed of approach increases or decreases rapidly .The rate of change in speed corresponds to the severity（激烈程度）of the turbulence.In a series of tests that began last month,a research jet flew repeatedly into disturbed air over the mountain ridges（山脉）near Pueblo , Colorado. The lidar detector spotted turbulence between 3 and 8 kilometers ahead,and its forecasts of strength and duration corresponded closely with the turbulence that the plane encountered.Bogue says that he had“a comfortable amount of time”to fasten his seatbelt. The researchers are planning to improve the lidar's range with a more powerful beam.The system could be installed on commercial aircraft in the next few years. What does“clear-air turbulence”in Paragraph 1 probably mean?A: A not very rough storm.B: Unexpected disturbed air.C: A kind of visible storm.D: A storm over mountain ridges.
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Please Fasten Your SeatbeltsSevere turbulence（湍流）can kill aircraft passengers. Now,in test flights over the RockyMountains , NASA（美国航空航天局）engineers have successfully detected clear-air turbulence up to 10 seconds before an aircraft hits it.Clear-air turbulence often catches pilots by surprise.Invisible to radar,it is difficult to forecast and can hurl（用力抛出去）passengers about the cabin. In December 1 997 , one passenger died and a hundred others were injured when unexpected rough air caused a United Airlines flight over the Pacific to drop 300 meters in a few seconds.However,passengers can avoid serious injury by fastening their seatbelts.“It is the only antidote（对策）for this sort of thing,”says Rod Bogue,project manager at NASA's Dryden FlightResearch Center in Edwards,California.The centre's new turbulence detector is based on lidar,or laser radar. Laser pulses are sent ahead of the plane and these are then reflected back by particles in the air. The technique depends on the Doppler effect.The wavelength of the light shifts according to the speed at which the particles are approaching. In calm air,the speed equals the plane's airspeed.But as the particles swirl（打漩）in rough air,their speed of approach increases or decreases rapidly .The rate of change in speed corresponds to the severity（激烈程度）of the turbulence.In a series of tests that began last month,a research jet flew repeatedly into disturbed air over the mountain ridges（山脉）near Pueblo , Colorado. The lidar detector spotted turbulence between 3 and 8 kilometers ahead,and its forecasts of strength and duration corresponded closely with the turbulence that the plane encountered.Bogue says that he had“a comfortable amount of time”to fasten his seatbelt. The researchers are planning to improve the lidar's range with a more powerful beam.The system could be installed on commercial aircraft in the next few years. In December 1997,a United Airlines flight hit unexpected rough air,_______.A: causing a lot of damage to the planeB: throwing its passengers out of the cabinC: resulting in heavy casualtiesD: forcing the pilot to make an emergency landing
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Please Fasten Your SeatbeltsSevere turbulence（湍流）can kill aircraft passengers. Now,in test flights over the RockyMountains , NASA（美国航空航天局）engineers have successfully detected clear-air turbulence up to 10 seconds before an aircraft hits it.Clear-air turbulence often catches pilots by surprise.Invisible to radar,it is difficult to forecast and can hurl（用力抛出去）passengers about the cabin. In December 1 997 , one passenger died and a hundred others were injured when unexpected rough air caused a United Airlines flight over the Pacific to drop 300 meters in a few seconds.However,passengers can avoid serious injury by fastening their seatbelts.“It is the only antidote（对策）for this sort of thing,”says Rod Bogue,project manager at NASA's Dryden FlightResearch Center in Edwards,California.The centre's new turbulence detector is based on lidar,or laser radar. Laser pulses are sent ahead of the plane and these are then reflected back by particles in the air. The technique depends on the Doppler effect.The wavelength of the light shifts according to the speed at which the particles are approaching. In calm air,the speed equals the plane's airspeed.But as the particles swirl（打漩）in rough air,their speed of approach increases or decreases rapidly .The rate of change in speed corresponds to the severity（激烈程度）of the turbulence.In a series of tests that began last month,a research jet flew repeatedly into disturbed air over the mountain ridges（山脉）near Pueblo , Colorado. The lidar detector spotted turbulence between 3 and 8 kilometers ahead,and its forecasts of strength and duration corresponded closely with the turbulence that the plane encountered.Bogue says that he had“a comfortable amount of time”to fasten his seatbelt. The researchers are planning to improve the lidar's range with a more powerful beam.The system could be installed on commercial aircraft in the next few years. The turbulence detector can tell the severity of the turbulence by measuring_______.A:.the speed of the planeB:.the speed of the lightC:.the number of particles in the airD:.the changes of the particles' speed
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Please Fasten Your SeatbeltsSevere turbulence（湍流）can kill aircraft passengers. Now,in test flights over the RockyMountains , NASA（美国航空航天局）engineers have successfully detected clear-air turbulence up to 10 seconds before an aircraft hits it.Clear-air turbulence often catches pilots by surprise.Invisible to radar,it is difficult to forecast and can hurl（用力抛出去）passengers about the cabin. In December 1 997 , one passenger died and a hundred others were injured when unexpected rough air caused a United Airlines flight over the Pacific to drop 300 meters in a few seconds.However,passengers can avoid serious injury by fastening their seatbelts.“It is the only antidote（对策）for this sort of thing,”says Rod Bogue,project manager at NASA's Dryden FlightResearch Center in Edwards,California.The centre's new turbulence detector is based on lidar,or laser radar. Laser pulses are sent ahead of the plane and these are then reflected back by particles in the air. The technique depends on the Doppler effect.The wavelength of the light shifts according to the speed at which the particles are approaching. In calm air,the speed equals the plane's airspeed.But as the particles swirl（打漩）in rough air,their speed of approach increases or decreases rapidly .The rate of change in speed corresponds to the severity（激烈程度）of the turbulence.In a series of tests that began last month,a research jet flew repeatedly into disturbed air over the mountain ridges（山脉）near Pueblo , Colorado. The lidar detector spotted turbulence between 3 and 8 kilometers ahead,and its forecasts of strength and duration corresponded closely with the turbulence that the plane encountered.Bogue says that he had“a comfortable amount of time”to fasten his seatbelt. The researchers are planning to improve the lidar's range with a more powerful beam.The system could be installed on commercial aircraft in the next few years. The last paragraph tells us,among other things,that_______.A: the lidar detector needs improvementB: many airlines are interested in the systemC: passengers often forget to fasten their seatbeltsD: the lidar detector can be used in a wide range of areas
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Women with AIDSFor a long time women with HIV were ignored because the focus was totally on HIV men.The gay community was very much in sight and vocal and successfully got support for its cause.Now we are rapidly approaching the point where about one haff of all AIDS cases in the. world are women. But no one is taking this dangerously high level of infection among women seriously enough.Women usually have a worse time dealing with HIV than men do.In most cases,the woman is taking care of children as well as her sick partner. She may not even have time to take care of herself. The HIV-positive woman ends up shouldering the family as well as her own personal problems. Men,however,are usually the ones who have insurance income and access to doctors.They get care.Women often do not.The discrimination against HIV-positive women is simply terrible.They are likely to be more inactive than men in the home and workplace because too many people think that women are the cause of the disease.This is not at all true.They get it from a man.They don't just simply have HIV.Of course,there's a social discrimination against all people with HIV.They are scared that other people will know they are HJV-positive and that they will,therefore be discriminated against. For example,it's very difficult for people with HIV to travel.They are not allowed to enter many countries,including the United States,China and Russia.The biggest difficulty an HIV-positive woman must face is the isolatjon.Once the woman knows she's HIV-positive,she lives in fear that other people will find out.She's so frightened she will go into hiding,into an isolated place by herself. It's not at all uncommon to meet a woman who has been HIV-positive for nearly 10 years and has never told anyone,except her doctor. And the resulting stress is enough to make her sick.But HIV-positive women who get support,who can discuss their trouble and then do something about it一whether that means taking better care of themselves or going to the United Nations to struggle for their rights一are likely to live longer. Active women don't die out of shame in a corner. This happens to too many HIV-positive women.Isolation is the biggest difficulty for HIV-positive women.A:Right B:Wrong C:Not mentioned
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Please Fasten Your SeatbeltsSevere turbulence（湍流）can kill aircraft passengers.Now,in test flights over the Rocky Mountains, NASA（美国航空航天局）engineers have successfully detected clear-air turbulence up to 10 seconds before an aircraft hits it.Clear-air turbulence often catches pilots by surprise.Invisible to radar,it is difficult to forecast and can hurl（用力抛出去）passengers about the cabin.In December 1997 , one passenger died and a hundred others were injured when unexpected rough air caused a United Airlines flight over the Pacific to drop 300 meters in a few seconds.However,passengers can avoid serious injury by fastening their seatbelts."It is the only antidote（对 策）for this sort of thing,"says Rod Bogue, project manager at NASA's Dryden Flight Research Center in Edwards,California.The Center's new turbulence detector is based on lidar,or laser-radar.Laser pulses are sent ahead of the plane and these are then reflected back by particles in the air.The technique depends on the Doppler Effect（多普勒效应）.The wavelength of the light shifts according to the speed at which the particles are approaching.In calm air,the speed equals the plane's airspeed.But as the particles swirl（打漩） in rough air,their speed of approach increases or decreases rapidly.The rate of change in speed corresponds to the severity（激烈程度）of the turbulence.In a series of tests that began last month,a research jet flew repeatedly into、 disturbed air over the mountain ridges（山脉）near Pueblo , Colorado.The lidar detector spotted turbulence between 3 and 8 kilometers ahead, and its forecasts of strength and duration corresponded closely with the turbulence that the plane encountered.Bogue says that he had"a comfortable amount of time"to fasten his seatbelt.The researchers are planning to improve the lidar's range with a more powerful beam.The system could be installed on commercial aircraft in the next few years.The last paragraph tells us,among other things,that____＿.A:the lidar detector needs improvementB:many airlines are interested in the systemC:passengers often forget to fasten their seatbeltsD:the lidar detector can be used in a wide range of areas
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Please Fasten Your SeatbeltsSevere turbulence（湍流）can kill aircraft passengers.Now,in test flights over the Rocky Mountains, NASA（美国航空航天局）engineers have successfully detected clear-air turbulence up to 10 seconds before an aircraft hits it.Clear-air turbulence often catches pilots by surprise.Invisible to radar,it is difficult to forecast and can hurl（用力抛出去）passengers about the cabin.In December 1997 , one passenger died and a hundred others were injured when unexpected rough air caused a United Airlines flight over the Pacific to drop 300 meters in a few seconds.However,passengers can avoid serious injury by fastening their seatbelts."It is the only antidote（对 策）for this sort of thing,"says Rod Bogue, project manager at NASA's Dryden Flight Research Center in Edwards,California.The Center's new turbulence detector is based on lidar,or laser-radar.Laser pulses are sent ahead of the plane and these are then reflected back by particles in the air.The technique depends on the Doppler Effect（多普勒效应）.The wavelength of the light shifts according to the speed at which the particles are approaching.In calm air,the speed equals the plane's airspeed.But as the particles swirl（打漩） in rough air,their speed of approach increases or decreases rapidly.The rate of change in speed corresponds to the severity（激烈程度）of the turbulence.In a series of tests that began last month,a research jet flew repeatedly into、 disturbed air over the mountain ridges（山脉）near Pueblo , Colorado.The lidar detector spotted turbulence between 3 and 8 kilometers ahead, and its forecasts of strength and duration corresponded closely with the turbulence that the plane encountered.Bogue says that he had"a comfortable amount of time"to fasten his seatbelt.The researchers are planning to improve the lidar's range with a more powerful beam.The system could be installed on commercial aircraft in the next few years.What does"clear-air turbulence"in Paragraph 1 probably mean?A:A not very rough storm.B:Unexpected disturbed air.C:A kind of visible storm.D:A storm over mountain ridges.
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Please Fasten Your SeatbeltsSevere turbulence（湍流）can kill aircraft passengers.Now,in test flights over the Rocky Mountains, NASA（美国航空航天局）engineers have successfully detected clear-air turbulence up to 10 seconds before an aircraft hits it.Clear-air turbulence often catches pilots by surprise.Invisible to radar,it is difficult to forecast and can hurl（用力抛出去）passengers about the cabin.In December 1997 , one passenger died and a hundred others were injured when unexpected rough air caused a United Airlines flight over the Pacific to drop 300 meters in a few seconds.However,passengers can avoid serious injury by fastening their seatbelts."It is the only antidote（对 策）for this sort of thing,"says Rod Bogue, project manager at NASA's Dryden Flight Research Center in Edwards,California.The Center's new turbulence detector is based on lidar,or laser-radar.Laser pulses are sent ahead of the plane and these are then reflected back by particles in the air.The technique depends on the Doppler Effect（多普勒效应）.The wavelength of the light shifts according to the speed at which the particles are approaching.In calm air,the speed equals the plane's airspeed.But as the particles swirl（打漩） in rough air,their speed of approach increases or decreases rapidly.The rate of change in speed corresponds to the severity（激烈程度）of the turbulence.In a series of tests that began last month,a research jet flew repeatedly into、 disturbed air over the mountain ridges（山脉）near Pueblo , Colorado.The lidar detector spotted turbulence between 3 and 8 kilometers ahead, and its forecasts of strength and duration corresponded closely with the turbulence that the plane encountered.Bogue says that he had"a comfortable amount of time"to fasten his seatbelt.The researchers are planning to improve the lidar's range with a more powerful beam.The system could be installed on commercial aircraft in the next few years.In December 1997,a United Airlines flight hit unexpected rough air______.A:causing a lot of damage to the planeB:throwing its passengers out of the cabinC:resulting in heavy casualtiesD:forcing the pilot to make an emergency landing
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Please Fasten Your SeatbeltsSevere turbulence（湍流）can kill aircraft passengers.Now,in test flights over the Rocky Mountains, NASA（美国航空航天局）engineers have successfully detected clear-air turbulence up to 10 seconds before an aircraft hits it.Clear-air turbulence often catches pilots by surprise.Invisible to radar,it is difficult to forecast and can hurl（用力抛出去）passengers about the cabin.In December 1997 , one passenger died and a hundred others were injured when unexpected rough air caused a United Airlines flight over the Pacific to drop 300 meters in a few seconds.However,passengers can avoid serious injury by fastening their seatbelts."It is the only antidote（对 策）for this sort of thing,"says Rod Bogue, project manager at NASA's Dryden Flight Research Center in Edwards,California.The Center's new turbulence detector is based on lidar,or laser-radar.Laser pulses are sent ahead of the plane and these are then reflected back by particles in the air.The technique depends on the Doppler Effect（多普勒效应）.The wavelength of the light shifts according to the speed at which the particles are approaching.In calm air,the speed equals the plane's airspeed.But as the particles swirl（打漩） in rough air,their speed of approach increases or decreases rapidly.The rate of change in speed corresponds to the severity（激烈程度）of the turbulence.In a series of tests that began last month,a research jet flew repeatedly into、 disturbed air over the mountain ridges（山脉）near Pueblo , Colorado.The lidar detector spotted turbulence between 3 and 8 kilometers ahead, and its forecasts of strength and duration corresponded closely with the turbulence that the plane encountered.Bogue says that he had"a comfortable amount of time"to fasten his seatbelt.The researchers are planning to improve the lidar's range with a more powerful beam.The system could be installed on commercial aircraft in the next few years.We can infer from the fifth paragraph that____＿.A:the lidar detector can successfully forecast turbulenceB:researchers are not sure about the effectiveness of the lidar detectorC:passenger planes will be used in further experimentsD:no more test flights are needed
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Please Fasten Your SeatbeltsSevere turbulence（湍流）can kill aircraft passengers.Now,in test flights over the Rocky Mountains, NASA（美国航空航天局）engineers have successfully detected clear-air turbulence up to 10 seconds before an aircraft hits it.Clear-air turbulence often catches pilots by surprise.Invisible to radar,it is difficult to forecast and can hurl（用力抛出去）passengers about the cabin.In December 1997 , one passenger died and a hundred others were injured when unexpected rough air caused a United Airlines flight over the Pacific to drop 300 meters in a few seconds.However,passengers can avoid serious injury by fastening their seatbelts."It is the only antidote（对 策）for this sort of thing,"says Rod Bogue, project manager at NASA's Dryden Flight Research Center in Edwards,California.The Center's new turbulence detector is based on lidar,or laser-radar.Laser pulses are sent ahead of the plane and these are then reflected back by particles in the air.The technique depends on the Doppler Effect（多普勒效应）.The wavelength of the light shifts according to the speed at which the particles are approaching.In calm air,the speed equals the plane's airspeed.But as the particles swirl（打漩） in rough air,their speed of approach increases or decreases rapidly.The rate of change in speed corresponds to the severity（激烈程度）of the turbulence.In a series of tests that began last month,a research jet flew repeatedly into、 disturbed air over the mountain ridges（山脉）near Pueblo , Colorado.The lidar detector spotted turbulence between 3 and 8 kilometers ahead, and its forecasts of strength and duration corresponded closely with the turbulence that the plane encountered.Bogue says that he had"a comfortable amount of time"to fasten his seatbelt.The researchers are planning to improve the lidar's range with a more powerful beam.The system could be installed on commercial aircraft in the next few years.The turbulence detector can tell the severity of the turbulence by measuring______.A:the speed of the planeB:the speed of the lightC:the number of particles in the airD:the changes of the particles'speed
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One of the main advantages of a graphite-furnace atomizer is that（）A、It requires only very small quantities of a sampleB、It requires metal.ions in aqueous solutionC、It does not produce background emission like a flameD、It does not get hot like a flame
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Which one of the following ions would give a basic solution upon addition to water？（）A、NH4+B、Na+C、C2H3O2-D、NO3-
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单选题According to a recent research， the old are more than twice as likely to have a positive attitude to life___ the young.A
asB
thanC
whileD
until
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单选题If over a period of weeks the air-box pressure of a turbo-charged, diesel engine, operating at full load, appears to be dropping off, the cause can be （）.A
open air-box drainsB
loss of cooling water to the diffuserC
gradual fouling of the air filtersD
improperly timed exhaust valves
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单选题Recent studies have suggested that weight training _____.A
has become an essential part of people’s lifeB
may well affect the health of the traineesC
will attract more people in the days to comeD
contributes to health improvement as well
考题
单选题The statement that “the people own the air” implies that _____.A
citizens have the right to insist on worthwhile television programsB
television should be socialized to cater to the nation’s whimsC
the government may build above present structuresD
the people own nothing, for air is worthless
考题
单选题Which of the following statements describes the function of an air compressor intake filter?（）A
Protects against suction valve floatB
Provides a positive pressure on the air inlet valvesC
Prevents lubricating oil contamination of the compressed air supplyD
Protects against the damaging effects of airborne solid particles
考题
单选题At ground level, nitrous oxides are bad enough, but when up high, atmospherically they bond with free ions to create dangerous smog particles.A
but when up high, atmospherically theyB
however, it is in the upper atmosphere in which it mayC
but in the upper atmosphere, theyD
however, but once in the upper atmosphere it is known toE
as in the upper atmosphere they
考题
单选题One of the main advantages of a graphite-furnace atomizer is that（）A
It requires only very small quantities of a sampleB
It requires metal.ions in aqueous solutionC
It does not produce background emission like a flameD
It does not get hot like a flame
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