What exactly are lewis acids and lewis bases?

Lewis acid are substance that contain H⁺ ion

for example;  

H₂o ⇒ H⁺ +  O₂

Lewis base are substance that contains OH⁻ ion

for example

NaOH ⇒ Na⁺  +  OH⁻

Lewis acid is  any substance, such as the H+ ion, that can accept a pair of nonbonding electrons. In other words, a Lewis acid is an electron-pair acceptor. e.g NH4+ and H3O.

A Lewis base is any substance, such as the OH- ion, that can donate a pair of nonbonding electrons. A Lewis base is therefore an electron-pair donor. e.g Water (H2O)

they are all solids.

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.