why might the melting point of the crystals obtained in this experiment be close to but below one of the reference melting points and melt slowly over several degrees

hello the experiment related to your question is missing but I will provide a more general answer within the scope of your  question

answer :

presence of Impurities

Explanation:

The melting point of the crystals as obtained in the experiment will be close to but below reference melting points and will also melt slower because of the presence of impurities in the compound

Impurities alter the melting and freezing points from ideal freezing and melting points of compounds

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.