gwd-29-9?(看过讨论贴，仍有不明白的地方）

hopefaith001

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?

                    

1. 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.
           
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.
           
3. 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.
           
4. 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. 这题的推理过程是因果的。那么按照lawyer_1对于weaken题的总结，这个题是属于哪种weaken的方式呢？还是说这个题不是不属于特殊的这四类呢？

因果型结论：即原文给出两件事，然后得出结论说是一件事（因）导致另一件事（果）。WEAKEN该结论的方法包括：A。是其他原因或可能导致该结果。B。割断因果：或有因无果或有果无因。C。因果颠倒了。D显示因果关系的资料不准确。