17. The choose the answer that is correct about the Earth's mantle. made of magnesium, iron, and calcium

made of rocky materials and water

made of the same rocky materials as the crust

made mostly of iron and nickel

a sequence is a function whose domain is the set of natural numbers.

natural numbers are all the negative and positive integers

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.