[求助]三道GWD逻辑不太明白，谁帮我解答一下？

第一个问题：

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.
5. 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.
6. 答案是E

第二个问题：

In order to evaluate the argument, it would be most helpful to determine which of the following?

1. Whether zinc is effective only against colds, or also has an effect on other virally caused diseases
2. Whether there are remedies that do not contain zinc but that, when taken orally, can reduce the duration of colds
3. Whether people who frequently catch colds have a zinc deficiency
4. Whether either the zinc gel or the lozenges contain ingredients that have an impact on the activity of the zinc
5. Whether the zinc gel has an effect on the severity of cold symptoms, as well as on their duration
6. 答案是D

第三个问题：

If the statements above are true, then it is also possible that in Patton City

1. the number of days with heavy rainfall was lower in 1990 than in 1910

2. the number of days with some rainfall, but no more than two inches, was the same in 1990 as in 1910
3. the number of days with some rainfall, but no more than two inches, was higher in 1990 than in 1910
4. the total number of inches of rain that fell on days with moderate rainfall in 1990 was more than twice what it had been in 1910
5. the average amount of rainfall per month was lower in 1990 than in 1910
6. 答案是A

各位NN麻烦解答一下！谢谢！