19.9% of all the isotopes of an element have a mass of 9.93 amu and 80.1% have a mass of 10.94 amu. What is the average mass of this element?

the answer is na (sodium)

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.