PT 63 S1 Q2

Jocko, a chimpanzee, was once given a large bunch ofbananas by a zookeeper ... ...

Which one of the following, if true, most seriously calls into question the zookeeper’s conclusion?
(A) Chimpanzees utter food barks only when their favorite foods are available.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in June 2011 LSAT (PT 63): Logical Reasoning A