prep一道CR有些不懂

1.       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.

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.

weaken题

答案是A,但是我觉得Kill whales就算去找别的food source，也不能肯定一定是去找sea otters了吧？

 但是对于答案B，和OG里好多题的本质一样，就是直接削弱事实，本省所说的decrease of seaotter population根本其实就不存在，我觉得是正确的答案啊，

请大家指教啊：）谢谢