Do bubbles, heat, formation of a solid always mean a reaction has taken place? Can you think of examples when they do not? What may be happening instead?

A chemical reaction always results in a new substance. A physical reaction only changes the physical properties of the reactants. For example, when you boil a pot of water, bubbles are formed and the water heats up. However, this is not a chemical reaction because the liquid water evaporates and becomes water vapor, a gas. A new substance is never formed.

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.