OFFICIAL EXPLANATION

The situation in the stimulus is that vervet monkeys use different calls depending on where predators come from. The correct answer must explain why the calls are different (again, difference versus similarity is an issue). Note that the stimulus does not contain a true paradox, just an odd situation that is presented without explanation.

Answer choice (A): This answer states that vervet monkeys vary the calls in order to indicate the number of predators, but the answer does not explain why different calls are used for land versus air predators. This answer is attractive because it shows that different calls can be used to indicate different things, but it is wrong because it does not explain the behavior of the monkeys as described in the stimulus.

Answer choice (B): This answer addresses only land-based predators and does not explain the difference described in the stimulus.

Answer choice (C): This answer states that the predators using land attacks are different from the predators using air attacks, but this information does not explain why vervet monkeys use different calls to indicate that fact.

Answer choice (D): This is the correct answer. Because vervet monkeys react to predators in different ways, they would need to know if the predator was coming by land or air. Hence, the different calls are used to tell the monkeys whether they should climb trees or dive into the foliage. Since this answer explains the behavior of vervet monkeys, this answer is correct.

Answer choice (E): The diet of selected predators of vervet monkeys is irrelevant and does not help explain why vervet monkeys use different calls depending on the direction of the attack.
_________________

Vervet monkeys use different alarm calls to warn each other of nearby predators, depending on whether the danger comes from land or from the air.

Which one of the following, if true, contributes most to an explanation of the behavior of vervet monkeys described above?

Why different alarms for different nature of the attack?
- Maybe they take a different course of action for different types of attacks.

A. By varying the pitch of its alarm call, a vervet monkey can indicate the number of predators approaching. But this option doesn't throw light on the need of having two different alarms.

B. Different land-based predators are responsible for different numbers of vervet monkey deaths. This option doesn't contribute to the nature of the vervet monkey mentioned in the argument.

C. No predators that pose a danger to vervet monkeys can attack both from land and from the air. This means the set of land attackers is disjoint from the set of aerial attackers. But this doesn't tell us anything about having two different alarms. If they have only one way to escape/avoid the attack, two different alarms don't add anything.

D. Vervet monkeys avoid land-based predators by climbing trees but avoid predation from the air by diving into foliage. If they take two totally different actions depending upon the nature of the attack, it becomes necessary that they are warned differently. So they must use different alarms in order to let the other members know what action the members must take.

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. Doesn't contribute toward explaining the behavior of the vervet company.

Thus, option D.

obvious (D) - it helps understand why the alarms made by monkeys are different
D. Vervet monkeys avoid land-based predators by climbing trees but avoid predation from the air by diving into foliage.

Presumably this is a paradox question. If so, what is the paradox?
_________________

i did not understand one thing - option D is not talking about "signals" . It is weakening - by telling its not signal , but actions. I think Option C strengthens? Could you please help me?

although this question is grouped as a paradox question, it does not really have one.

The official answer expands on this -

The answer stem should help explain this odd situation.