ｘｄｆ绿皮　２０９　大全里搜不出来此题

没有在大全里看到这道题，不知是没有还是我没搜到。打出来。

209

Manatees, aquatic mammals inhabiting Florida's river 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 water is being required to maintain very low speeds. Unfortunately, manatees are unable to hear low-pitched wounds and a boat's sound lower 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?

209

Manatees, aquatic mammals inhabiting Florida's river 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 water is being required to maintain very low speeds. Unfortunately, manatees are unable to hear low-pitched wounds and a boat's sound lower 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?

1. The area 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
2. 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

b说的是食物什么的， 和题目的论证没有关系的， 是无关的。

3. Over the last several decade, boat traffic in Florida's coastal water has been increasing almost continuously and now represents the greatest threat to the endangered manatee population
4. The sound of boat engine generally travels much further under water than it does through the air
5. When experimenters exposed manatees to the recorded sounds of boats moving at various speed, the creatures were unable to discern the sounds over normal back ground noise.