When classifying parts of speech, which word would be identified as an adverb?

The word identified as an adverb in this context is "yesterday." Adverbs are words that typically modify verbs, adjectives, or other adverbs, often providing information about time, manner, place, or degree. "Yesterday" specifically indicates a time reference, thus modifying a verb by clarifying when an action took place.

In contrast, "Monday" is a noun that signifies a specific day of the week, while "football" is also a noun, referring to a sport or ball used in the game. The word "for" is a preposition, which connects nouns or pronouns to other words in a sentence, but does not function as an adverb. Each of these options serves a different grammatical purpose, but "yesterday" specifically fits the role of an adverb by relating to the timing of an action.