According to the selection, which of the two following are the first signs that a tornado is starting to form

the rigid outer part of the earth, consisting of the crust and upper mantle is the lithosphere.     answer   crust and outer part of the mantle.

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.