请教 GWD-29-Q9

ashleych

28: GWD-29-Q9
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.

题目里说因为Manatees听不见低音，而船开得越慢声音越低，所以这种方法会把事情搞得更糟。
想问下B项的问题，说Manatees喜欢吃的东东是长在静水里的，所以明显慢船是有好处的，这不就削弱结论了么？还望NN指点~

LeannaChina

提干结论：船开慢所导致的引擎声变低会使撞到海牛这种情形变得更糟糕。
那么质疑就是 声音变低会不会让事情变得更糟？能够对这一选项回答不会的就为正确答案。

B：因为海牛吃的东西在静止的水中长的最好，海牛就会被快速移动的船打扰。-〉和声音无关，没有结论
E：实验人员实验出海牛对于声音的因素不敏感。--〉声音大小对于海牛没有影响，因此声音变低不会让事情更糟。

Serena11457

正确答案：E
注意B选项，原题结论是this approach may in fact make things worse rather than better，这里的things指的是Manatees frequently killed in collisions with boats这件事，B选项削弱的是如果降低速度那么M的死亡率会上升这件事，因此B选项属于无关选项！

veralove3271

The passage is about manatees dying of killing, not dying of hunger.