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?

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 substantial numbers of sea otters migrated to other
locations from the North Pacific in the 1980’s.

C.
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.
     

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.