It's an adverb.
The word yesterday is an adverb.
Did and attend are verbs, and not is an adverb.
In the sentence, "Which is his sister?", "which" is an interrogative pronoun.
Why is the beginning of a interrogative sentence.
Noun--however, many words have several possible parts of speech; please submit the Whole Sentence when asking for part of speech--cannot be sure without seeing how it is used in the sentence, as that's what determines the part of speech.
Yesterday is a noun in that sentence.
Yesterday is an adverb in that sentence.
In the sentence "yesterday the leaves hung on the tree," "yesterday" is functioning as an adverb modifying the verb "hung."
She gave a terrific speech yesterday.
Practice is a noun in that sentence. It's the object of the preposition "for".
Cognition refers to the mental processes associated with acquiring knowledge and understanding.
Verb
Where did you attend college? (You did attend college where?)where - adverb, modifies the verb 'did attend';did - auxiliary verb;you - personal pronoun, subject of the sentence;attend - main verb;college - noun, direct object of the verb 'did attend'.
What college did he attend? (He did attend what college?)what - interrogative pronoun, functioning as a determiner;college - noun, direct object of the verb 'did attend';did - auxiliary verb;he - personal pronoun, subject of the sentence;attend - main verb.
The word yesterday is an adverb.
Did and attend are verbs, and not is an adverb.
Dad was thrilled to hear about my acceptance to St. Louis University. She won the mayoral election yesterday and gave her acceptance speech this morning.