[求助]GWD 一道削弱 一道归纳

In the late 1980’s, the population of sea otters in the North Pacific Ocean began to decline.  Of the two plausible explanations for the decline—increased predation by killer whales or disease—disease is the more likely.  After all, a concurrent sharp decline in the populations of seals and sea lions was almost certainly caused by a pollution-related disease, which could have spread to sea otters, whereas the population of killer whales did not change noticeably.

Which of the following, if true, most seriously weakens the reasoning?

1. Killer whales in the North Pacific usually prey on seals and sea lions but will, when this food source is scarce, seek out other prey.

2. There is no indication that substantial numbers of sea otters migrated to other locations from the North Pacific in the 1980’s.

3. Along the Pacific coast of North America in the 1980’s, sea otters were absent from many locations where they had been relatively common in former times.

4. Following the decline in the population of the sea otters, there was an increase in the population of sea urchins, which are sea otters’ main food source.

5. The North Pacific populations of seals and sea lions cover a wider geographic area than does the population of sea otters.

答案是A  感觉B也是削弱啊？？？！！！

还有这道题

If the statements above are true, which of the following conclusions can be properly drawn?

1. United States manufacturers of tobacco products had higher profits in 1976 than in 1973.

2. Per capita consumption of cigarettes in the United States was lower in 1976 than in 1973.

3. The proportion of nonsmokers in the United States population dropped slightly between 1973 and 1976.

4. United States manufacturers of tobacco products realize a lower profit on cigarettes than on chewing tobacco.

5. A large percentage of United States smokers switched from cigarettes to chewing tobacco between 1973 and 1976.

答案是B  看到题目是已经有点晕了 看完选项就彻底不知道怎么算出来的了（我开始怀疑自己的智商了）

谢谢大家先

为何没人帮我

自己UP 一下