[問題]GWD 29-Q9

[bonus]

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.

Answer: E

[bonus]

原文的結論是：這個方法會使情況變得更糟。削弱：沒有使情況變得更糟。
原文的推理是：船速降低後，音調變小，所以動物聽不見了（船快的時候能聽見），所以更容易撞船了，因此情況變更糟了。
E說，船在各個速度下，這動物其實根本分不出船的聲音和其他聲音（可以理解為這動物就是聾的），所以船快船慢，這動物被船撞得幾率是一樣的，因此就不能說這個計劃使情況變糟了。
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轉自CD大牛

[amyliang]

為什麼d不行呢?

[Huang Hsin-Yi]

因為manatees are unable to hear low-pitched sounds and a boat’s sound lowers in pitch as the boat slows,因此引擎聲音傳的遠不遠,便是無關選項

但要推出E也真不容易~~~~

[Huang Hsin-Yi]

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