题目选项分析

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?

【选项】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.