The diagram shows a roller-coaster track. Assume that the system is closed. At point D, the roller-coaster car is at the top of the vertical loop. Which chart best shows the relative amounts of potential and kinetic energy of a roller-coaster car at point D?

the answer is b because, investigating whether another species of moth also drinks tears might be interesting, but it would not directly explain why this species of moth does.

to explain why this species of moth drinks tears, the scientist could ask: "what nutrients that moths need are in elephant tears? "

the scientist could experiment with moth repellent or oter ways to keep the moths away, but that would not answer his original question.