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Manatees, aquatic mammals inhabiting Florida’s rivers andcoastal waters, swim close to the surface and are frequently killed incollisions with boats. To address theproblem, boat traffic in manatee-populated waters is being required to maintainvery low speeds. Unfortunately, manateesare unable to hear low-pitched sounds and a boat’s sound lowers in pitch as theboat slows. Therefore, this approach mayin fact make things worse rather than better. Which of the following, if true, castsmost doubt on the conclusion? A. The areas where boats would have to maintainlow speeds were decided partly on the basis of manatee-population estimates andpartly from numbers of reported collisions between manatees and boats. B. Because the water hyacinth that manateesfeed on grows best in water that is nearly still, water hyacinth beds can bedisturbed or damaged by fast-moving boat traffic. C. Over the last several decades, boat trafficin Florida’scoastal waters has been increasing almost continuously and now represents thegreatest threat to the endangered manatee population. D. The sound of a boat engine generally travelsmuch further under water than it does through the air. E. When experimenters exposed manatees to therecorded sounds of boats moving at various speeds, the creatures were unable todiscern the sounds overnormal background noise.
正确答案是E，但是我感觉B也对啊。M的食物hyainth在比较静的水中长得好，那船速慢了，H长得好，M的食物多，不是削弱了结论“减速不好”？
我记得有一个非常相似的题就是采用B选项的方法证明好处的。
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发表于 2013-7-26 22:20:07
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