(b) Potassium and sodium are kept in dark reagent bottles filled with paraffin oil.
Explain why.​

these metals are stored in kerosene because kerosene contains no water and protects these metals from being exposed to any moisture in the air that would cause these metals to react, potentially violently.

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.