What part of speech is "flew" in the sentence: "The swift bird flew by"?

In the sentence "The swift bird flew by," the word "flew" functions as a verb. Verbs are words that express actions, occurrences, or states of being. In this case, "flew" describes the action that the bird is performing; it indicates the movement of the bird through the air. The use of "flew" is the past tense of the verb "to fly," further reinforcing its role as an action word.

The other options do not apply because an adjective describes a noun, a noun represents a person, place, thing, or idea, and a pronoun takes the place of a noun. In this context, "flew" clearly manifests the action being taken by the subject "the swift bird."