Final answer:
In the sentence 'He drives a fast car', the word 'fast' is an adjective. It is used to describe the noun 'car', not the verb 'drives'. Therefore, it is not an adverb in this context.
Step-by-step explanation:
In the sentence 'He drives a fast car', the word 'fast' serves as an adjective. It describes the noun 'car'. An adjective is a part of speech that modifies or describes a noun or a pronoun. In other words, in the context of this sentence, 'fast' is used as an adjective to give us more information about the car, which is the object of the sentence. An adverb, on the other hand, modifies a verb, an adjective, or another adverb. But in this case, 'fast' is not modifying the verb 'drives' but the noun 'car'.
Learn more about Adjectives and Adverbs