求教：PREP中有关sea otters的题目

   In the late 1980s, the population of sea otters in the North Pacific began to decline. There are two plausible explanations for the decline: predation, possibly by killer whales, or disease. Of these two, disease is the more likely, since a concurrent sharp decline in populations of seals and sea lions is believed to have been caused by disease, and diseases that infect these creatures are likely to be able to infect sea otters also.

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

A. 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.

B. There is no indication that the sea otter population at any North Pacific location declined in the 1980s because of substantial numbers of sea otters migrating to other locations.

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

D. 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.

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

为什么答案选A呢?我没想明白...呼唤NN~

题目提供了两种原因：There are two plausible explanations for the decline: predation, possibly by killer whales, or disease.

并说是由于disease，而问题要求weaken

A说明因为disease,seals and sea lions 都病了，所以Killer whales in the North Pacific 的食物就减少了，只能 seek out other prey，也就是sea otters。就削弱了sea otters是因为diseas这个结论。