单选题

A By the end of this century.

B By the first half of this century.

C By the second half of this century.

D In the middle of this century.

解析：
[考点]细节题。录音提到，大多数科学家认为最大化的警告将会在本世纪后50年产生。
【听力原文】
　　With the development of science, scientists have discovered more about the world. Scientists say world coastal areas must prepare now for [33] a rise in sea levels. No matter what action is taken, scientists say there are already enough [34] greenhouse gases in the atmosphere to cause a major warning. As a result, scientists and government officials are focusing on how society might adapt to rising sea levels, changing agricultural zones, changing climates and other problems.
　　Already, state and local governments along the coast of the United States are starting to plan for a possible long-term rise in the sea level, and a few have taken action to cope with it. Agricultural researchers are developing [35] heat-resistant and draught-resistant crops that might replace traditional crops if the climate changes. How long it will take for maximum warming to be reached is uncertain because the oceans slow such warming. Most scientists expect the maximum warming to take place [36] by the second half of this century.
　　If levels of greenhouse gases in the atmosphere double, sea levels will rise; estimates of the average rise are from 1.5 feet to 6.5 feet. Some leading experts expect a rise of 1 meter, a little more than three feet.
Questions 33 to36 are based on the passage you have just heard.
33. What must world coastal areas prepare for according to scientists’ opinion?
34. According to the passage, what has caused the rise in sea levels?
35. What are the agricultural researchers developing?
36. When will the maximum warming take place?