Cacao is bitter when it is tasted.

The correct answer is: B. Cacao tastes bitter.

A. Cacao is bitter is a statement about the nature of cacao, not about the experience of tasting it.
C. Cacao’s taste is bitter is a similar statement, but it is in the possessive case, which is not necessary in this context.
D. Cacao tasted bitter is in the past tense, which does not make sense in this context, since the question is about the taste of cacao in general, not about a specific instance of tasting it.

B. Cacao tastes bitter is the only option that accurately describes the experience of tasting cacao. Cacao is a bitter-tasting substance, and this is the most common way to describe its taste.