PT 41 S1 Q8

Vervet monkeys use different alarm calls to warn each other of nearby predators, ... ...

Which one of the following, if true, contributes most to an explanation of the behavior of vervet monkeys described above?
(A) By varying the pitch of its alarm call, a vervet monkey can indicate the number of predators approaching.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in Practice Set: "Resolve/Explain" Questions, Set 1