Thanks for your question, @HillaryMaria. Let's first examine the stimulus.
Here, we are told that these monkeys use different kinds of alarm calls to warn each other about nearby predators, depending on whether the threat is coming at them from land or from air.
The question stem asks us to select the answer choice that would best explain this phenomenon.
Answer choice (D) does just that. If it is true that the monkeys respond differently to different predator threats based on whether those threats are coming at them from land vs. from air, then it makes sense that the monkeys use different kinds of alarm calls to warn each other (rather than the same kind of alarm call no matter what).
Hope this helps. Please let us know if you have any additional questions.
