An adverb modifies a ...

Noun or pronoun

Adverb or verb

Adjective or noun

Interjection or conjunction

In the English language, an adverb is a word that describes a verb, adjective or another adverb in a sentence.

Adverbs express a relation of place, time, circumstance, manner, etc.

Examples: Quietly, Quickly, far, close, etc,

Going with the definition, your best answer would be "Adverb or verb".