请教GWD-29-Q9

reddragon

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.

答案是E，我选的是D，并且还想了半天不明白，请高人帮忙敲打一下，多谢

EGHJUYMN

Manatees经常被船撞死，为了解决这个问题，在manatee繁殖的水域，船只需要维持一个非常低的速度。不幸的是，manatee无法听到low-pitched的声音，而船在低速时的声音lower in pitch。因此，这种方法事实上会使情况更糟。

D：船引擎的声音在水中比在空气中传得更远；（原题说manatee听不到low-pitched的声音，传得再远也没用呀）
E：试验中，将各种速度下船产生的声音放给manatee听，manatee没有办法区分背景音与船的声音。（无论船高速，中速，低速的声音，都被背景音给掩盖，manatee在有背景音的情况下，听不到boat的声音）

reddragon

明白了，多谢大人！

victoria820

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.选了B，当时觉得说到减速的话不会像以前高速行驶一样破坏M的食物，感觉是在说减速好。。

明白E对了，现在不知道怎么排除B呢？

zengzihao

觉得B项也很合理啊~有米有NN能帮忙解释下子啊~谢啦

anchoretes

我的第一感觉也是选b，
感觉b是质疑了结论，d是质疑了推导过程。

bettyofariN

water hyacinth beds 文中结论根本没有提到

LIANGSHAN

我觉得这道题让人混淆的是哪个是结论——是最后一句这个方法不行还是倒数第二句M在船满行的时候更听不到低调声音。通过研究选项发现结论是后者。

削弱题要找结论的茬。看选项E，M根本对船音没反应，很显然结论不成立。