A ball rolling down a hill will: keep rolling forever
roll until stopped by a force
gain potential energy

it should have an internal chamber and two thermometers sticking out of the top. the internal chamber will also be closed off from the outside.

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.