Explain the difference between an adjective phrase and an adverb phrase?

An adj phrase is a phrase that some uses to describe something and an adverb phrase is a phrase is a word group with the adverb as its main word.

your answer would be a verb. because they are "doing something"

the answer is:

when will (v) the books (n) be (v) due?

nouns refer to people (other than pronouns), places and things, whereas verbs describe actions and are usually part of the predicate of a sentence. finally, pronouns can work as nouns and identify the participants in speech.

in the example sentence, "will" is a verb part or auxiliary verb, "be" is an infinitive verb and "books" is a plural noun.