共用题干第一篇Plant GasScientists have been studying natural sources of methane（甲烷...

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问题共用题干第一篇

Plant Gas

Scientists have been studying natural sources of methane（甲烷，沼气）for decades but hadn't regarded plants as a producer, notes Frank Keppler, a geochemist（地球化学家）at the Max Planck Institute for Nuclear Physics in Heldelberg,Germany. Now Keppler and his colleagues find that plants,from grasses to trees,may also be sources of the greenhouse gas.This is really surprising, because most scientists assumed that methane production requires an oxygen-free environment.
Previously,researchers had thought that it was impossible for plants to make significant amounts of the gas. They had assumed that microbes（微生物）need to be in environments without oxygen to produce methane.Methane is a greenhouse gas, like carbon dioxide.Gases such as methane and carbon dioxide trap heat in Earth's atmosphere and contribute to global warming.
In its experiments, Keppler's team used sealed chambers（室，房间；腔）that contained the same concentration of oxygen that Earth's atmosphere has.They measured the amounts of methane that were released by both living plants and dried plant material,such as fallen leaves.
With the dried plants,the researchers took measurement at temperatures ranging from 30 degrees Celsius to 70 degrees C.At 30 degrees C.,they found,a gram of dried plant material released up to 3 nanograms（微克）of methane per hour(One nanogram is a millionth of a gram). With every 10-degree rise in temperature,the amount of methane released each hour roughly doubled.
Living plants growing at their normal temperatures released as much as 370 nanograms of methane per gram of plant tissue per hour. Methane emissions tripled when living and dead plant was exposed to sunlight.
Because there was plenty of oxygen available,it's unlikely that the types of bacteria(bacterium的复数，细菌）that normally make methane were involved. Experiments on plants that were grown in water rather than soil also resulted in methane emissions.That's another strong sign that the gas came from the plants and not soil microbes.
The new finding is an"interesting observation,"says Jennifer Y. King,a biogeochemist（生物地球化学家）at the University of Minnesota in St. Paul. Because some types of soil microbes consume methane,they may prevent plant-produced methane from reaching the atmosphere.Field tests will be needed to assess the plant's influence,she notes.

选项 What was scientists' understanding of methane? A:It was produced from plants. B:It was not a greenhouse gas. C:It was produced in oxygen-free environments. D:It traps more heat than any other greenhouse gas.

答案 C

解析短文的第一段和第二段都讲到，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．…
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项符合原文的意思，其他三个选项则不符合原文内容。
根据第四段和第五段的内容，只有D项是正确的说法。温度越高，沼气的释放量越大，有生命的植物释放的沼气量远大于干燥植物的释放量，在阳光下，它们的沼气释放量是正常情况下的3倍。
最后两段告诉我们，无论在封闭环境中还是在水中生长的植物都能释放沼气，封闭环境中的微生物消耗沼气，使沼气不至于进入大气中。所以选项A、B、C的内容均符合短文最后两段中作者的意思。D项内容短文中没有提到。
从最后一段的第二句可以找到本题的答案。

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共用题干第一篇Plant GasScientists have been studying natural sources of methane（甲烷...

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共用题干第一篇Plant GasScientists have been studying natural sources of methane（甲烷...