Even though technically all of these answers are correct, I still have to pick one as the incorrect answer. So, my answer is C. an adverb can be a noun.
A and B are definitely correct - adverbs are indeed words that describe verbs and tell us more about them (he runs fast). D is also correct as the word really is an adverb that modifies the adjective handsome. So we are only left with C as the correct answer.
