Answer: A) too.
Explanation: an adverb is a word or phrase that modifies or qualifies an adjective, verb, or other adverb or a word group, expressing a relation of place, time, circumstance, manner, cause, degree, etc. In the given sentence we can see two adverbs: "quickly" that modifies the verb "flies" indicating manner, and the adverb "too" that modifies the adverb "quickly" indicating degree.
