Why use absorption spectra not emission to identify gas?

It may seem remarkable that we can learn about the composition of distant stars by studying the light they emit. In fact, we can learn a great deal, not only about the chemical elements present, but also about physical conditions. The key is to spread the light out by color, producing a spectrum like the one shown in Fig. 1. This lab explores some of the basic ideas used to analyze spectra.

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.