In the sentence "She quickly finished her homework," the word "quickly" is identified as an adverb. This is determined by the following grammatical principles:
Adverbs are words that modify verbs, adjectives, or other adverbs. They typically answer questions about how, when, where, or to what extent an action occurs.
The word "quickly" specifies the manner in which the verb "finished" is executed, detailing the speed of her homework completion.
Consequently, "quickly" aligns with the definition of an adverb by modifying the verb "finished" and indicating the pace of the action.
The identified part of speech for "quickly" in this specific sentence is: Adverb.