Thomas wants to measure the temperature change that occurs when sodium hydroxide is dissolved in water
which is the best tool for this purpose?

answer:

a thermometer setted in the flask containing sodium hydroxide and water solution will measure the rise in temperature

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.