2. To test whether plants are a sot，roe of methane，the scientists created
A a oxygen-free environment.
B an environment with the same concentration of oxygen as the Earth has.
C a carbon dioxide-free environment.
D an environment filled with the greenhouse gas.
3. Which statement is true of the methane emissions of plants in the experiment？
A The lower the temperature，the higher the amount of methane emissions.
B I.iving plants release less methane than dried plants at the same temperature.
C When exposed to sunlight，plants stop releasing methane.
D The higher the temperature，the greater the amount of methane emissions.
4. Which of the following about methane is Not mentioned in the passage？
A Plants growing in soil release methane.
B Plants growing in water release methane.
C Soil microbes consume methane.
D Microbes in plants produce methane.
5. What is the beneficial point of some microbes consuming plant-produced methane？
A Methane becomes less poisonous.
B Methane is turned into a fertilizer.
C Less methane reaches the atmosphere.
D Air becomes cleaner.
答案与题解：
1. C 短文的第一和第二段都讲到，科学家过去曾经认为，沼气必须在无氧的环境中才能产生。注意，作者用的是过去式：Most scientists assumed that.……They had assumed that.……
2. B 第三段第一句说，科学家使用密封的房间来做实验，房间里氧气的浓度与地球大气中的氧气浓度相仿。所以B句符合原文的意思，其他三个选择则不符合原文内容。
3. D 根据第四和第五段的内容，只有D是正确的说法。温度越高沼气的释放量越高，有生命的植物释放的沼气远大于干植物的释放量，在阳光下，它们的沼气释放量是正常情况的三倍。
4. D 最后两段告诉我们，无论在土壤中还是在水中生长的植物都能释放沼气，土壤中的微生物消耗沼气，使沼气不至于进入空气。所以A、B、C的内容均符合短文最后两段中作者的意思。D的内容短文中没有提到。
5. C 最后一段的第二句可以找到本题的答案。