求助一逻辑题(迷惑)

１９.The large amounts of carbon dioxide now being released into the atmosphere by the burning of fossil fuels will not ,in fact,result in a greenhouse effectan increase in average global temperatures .Since plants use carbon dioxide in large quantities if the suplly is increased,they are able to grow larger and multiply more vigorously,and atmospheric carbon dioxide concentrations will eventually become stable.

Which of the following,if true,would most seriously weakens the conclusion that a greenhouse effect will not result from the current release of large amounts of carbon dioxide into the atmosphere?

A.The excepted rise in average global temperaturea has not yet been observed .

B.Ocean waters absorb carbon dioxide at a greater rate when the atmospheric concentrations of carbon dioxide is higher.

C.Since the beginning of the Industrial Revolution,increased atmospheric concentrations of carbon dioxide have resultes in improved agricultural productivity.

D.When plants decay,they produce methane,another gas that can have a marked greenhouse effet.

E.The fact that carbon dioxide levels have risen and fallen many times in the Earth's history suggests that there is some biological process that can reverse the greenhouse effect.

正确答案是Ｄ，但是题中要求weaken的是释放到大气中的二氧化碳不会引起温室效应．既然是要削弱这个结论，那就应该是要说明这个二氧化碳是应该会引起温室效应．但是我认为methane是个新名词，跟削弱的结论没什么关联啊．为什么是它呢？

题目说二氧化炭使plants张的快,那plants张的快么,就死的也多,那死后分解产生的methane也多,总的效果上还是会加重greenhouse的effect