BTW, you chopped off the end of answer (E) --- I had to find it on another site.
So, the vervet monkeys make a distinction --- one alarm for predators by land, and another for predators from the air. Why? Why two alarms? Why wouldn't just one generic alarm call --- "Predators!" ---- be sufficient?

(A) By varying the pitch of its alarm call, a vervet monkey can indicate the number of predators approaching.
The different calls distinguish the means by which the predator approaches, land or air, and has nothing to do with the number of predators. This completely changes the issue.

(B) Different land-based predators are responsible for different numbers of vervet monkey deaths.
If this were the case, we would expect different calls for different land-based predators --- this tells us nothing about the land/air distinction.

(C) No predators that pose a danger to vervet monkeys can attack both from land and from the air.
OK, this would mean there's no ambiguity in what each of the two calls means, but fundamentally doesn't explain why there would need to be two alarm calls instead of just one that means "predators!"

(D) Vervet monkeys avoid land-based predators by climbing trees but avoid predation from the air by diving into foliage.
Aha! The vervet monkeys take different evasive action, depending on whether the predator comes by air or by land --- thus, each alarm call would signal a unique evasive strategy appropriate to a predator from that medium. This make a great deal of sense.

(E) Certain land-based predators feed only on vervet monkeys, whereas every predator that attacks vervet monkeys from the air feeds on many different animals.
Whether other critters get eaten too is irrelevant to vervet monkeys trying to avoid getting eaten. The animal would not develop a difference in its alarm call to save some other species of animal.

The only sensible answer is (D).

Does all this make sense?

Mike
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Mike McGarry
Magoosh Test Prep