Why might it be useful to determine the elements that a planet or moon is made up of?

It may help us determine the hospitable planets where humans can migrate to when the earth becomes inhospitable. This study also helps us determine the composition of the universe and its evolution. It may also be of economic value to determine the elements that can be exploited for human development in the universe.

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.