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单选题
在制药时，为从溶液中提取抗菌素，要用加热的方法使水沸腾而除去水分，但抗生素不能在超过80℃的条件下提取，应采用的办法是（）。
A
增加容器内的气压，使水的沸点低于80℃
B
降低容器内的气压，使水的沸点低于80℃
C
缩短加热沸腾的时间
D
用微火加热使其沸腾
参考答案
参考解析
解析：
此题要求降低水的沸点才能提取抗菌素，根据沸点和气压的关系，气压越大，沸点越高，气压越小，沸点越低，所以答案为B。
更多 “单选题在制药时，为从溶液中提取抗菌素，要用加热的方法使水沸腾而除去水分，但抗生素不能在超过80℃的条件下提取，应采用的办法是（）。A 增加容器内的气压，使水的沸点低于80℃B 降低容器内的气压，使水的沸点低于80℃C 缩短加热沸腾的时间D 用微火加热使其沸腾” 相关考题
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difficult and terribleD
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loyalty of top performers is getting out-datedC
top performers care more about reputationsD
it's safer to stick to the traditional rules
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controller
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单选题请阅读 Passage 1,完成21-25小题。 Passage 1 Kimberley Asselin sits in a rocking chair in front of her 22 kindergartners, a glistening smile across her face as she greets them for the morning. Even at 9 a.m., she is effervescent and charismatic. Yet behind Asselin´s bright expression, her enthusiasm is fading. Asselin,24, is days away from finishing her first year as a teacher, the career of her dreams since she was a little girl giving arithmetic lessons on a dry-erase board to her stuffed bears and dolls. While she began the school year in Virginia´s Fairfax County full of optimism, Asselin now finds herself, as many young teachers do, questioning her future as an educator. What changed in the months between August and June? She says that an onslaught of tests that she´s required to give to her five-and six-year-old students has brought her down to reality. "It´ s more than a first-year teacher ever imagines," Asselin said."You definitely have a lot of highs and lows, and it keeps going up and down and up and down." New federal data that the Education Department released in April shows that about 10 percent of new teachers leave the profession within the first year on the job, and 17 percent leave within five years of starting. Though far lower than earlier estimates, it still means that many young educators bail from the classroom before they gain much of a foothold. For Asselin, testing has been the biggest stressor. The proliferation of testing in schools has become one of the most contentious topics in U.S.education. The exams can alter the course of a student´s schooling and can determine whether a teacher is promoted or fired. In Virginia, schools earn grades on state-issued report cards based on the scores students earn on mandatory end-of-year exams. The Fairfax County school system, one of the nation´s largest, boasts that its kindergarten students take part in coursework that exceeds the state´ s standards. Unlike most states, Virginia has never adopted the Common Core State Standards, but Virginia officials say that the state´ s academic standards are just as--or more--rigorous. Asselin said that means that even the youngest students in public school are trader an academic microscope, making kindergarten about far more than socialization and play time.According to the author, what kind of place is a kindergarten supposed to be?A
A place of academic training.B
A place of reading and writing.C
A place where there are no tests.D
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考题
单选题科学探究中猜想与假设的含义是（）A
根据对问题的逻辑分析找到问题的所有可能的答案B
以个人的直觉为主要依据.对问题成因和可能出现的结果所进行的发敖性思维C
根据个人的经验对问题的成因和可能出现的结果进行的随意的设想D
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考题
单选题What does the underlined word "them" in PARAGRAPH THREE refer to?A
Birds.B
Flowers.C
Food scrapes.D
Scavengers.
考题
单选题达尔文的“进化论”作为一项自然科学的巨大成就.也对人类社会的政治和思想观念产生了很大影响。下列分析正确的是（）。A
成为欧洲启蒙运动批判专制统治的思想武器B
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考题
单选题A
P点仍为明条纹B
P点为暗条纹C
不能确定P点是明条纹还是暗条纹D
无干涉条纹
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