一道逻辑，居然觉得没选项可选

serenashu

Manatees, aquatic mammals inhabiting Florida

’s rivers and coastal waters, swim close to the surface and are frequently killed in collisions with boats.To address the problem, boat traffic in manatee-populated waters is being required to maintain very low speeds.Unfortunately, manatees are unable to hear low-pitched sounds and a boat’s sound lowers in pitch as the boat slows.Therefore, this approach may in fact make things worse rather than better.

Which of the following, if true, casts most doubt on the conclusion?

A.The areas where boats would have to maintain low speeds were decided partly on the basis of manatee-population estimates and partly from numbers of reported collisions between manatees and boats.

B.Because the water hyacinth that manatees feed on grows best in water that is nearly still, water hyacinth beds can be disturbed or damaged by fast-moving boat traffic.

C.Over the last several decades, boat traffic in Florida

’s coastal waters has been increasing almost continuously and now represents the greatest threat to the endangered manatee population.

D.The sound of a boat engine generally travels much further under water than it does through the air.

E.When experimenters exposed manatees to the recorded sounds of boats moving at various speeds, the creatures were unable to discern the sounds over normal background noise.

这题我感觉没有一个选项可以选啊？

boboakira

选E。题目说因为船开的慢，引擎声音就比较低，导致海豹（？）听不见，因此降低速度会导致海豹更危险。
如果能证明海豹根本不是根据船声大小来躲避船害的，那题目的结论就削弱了。
E 的意思是说，实验表明，不管船发出什么速度的声波，海豹都无法辨别。因此可推断出，海豹和船相撞根本不是声音的缘故，结论就被削弱了

serenashu

恍然大悟~~谢谢楼上！！！