Manatees, aquatic mammals inhabiting Florida's rivers and coastal waters, swim close to the surface...

题目信息

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.

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正确答案： 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.

目的：降低海牛因撞船而死亡的几率从而保护海牛

方法：降低船速

因为：海牛无法听到低声波的声音

所以：此方法无法减少海牛死亡从而无效问削弱

A 该区域限制不限制船行速度取决于海牛的密度及事故发生率无关

B 有关海牛食物会遭到破坏无关

C 过去几十年海牛撞船案急剧上升成为威胁海牛的最大威胁无关

D 声音在水中会传播的更远，对比在空气中，因为海牛根本听不到低音，所以无效

E 正确。实验证明海牛对所有的声音摄入都无反应。则结论所提出的因为声音降低海牛无法识别，根本就是不成立的。削弱

笔记