"_____ walk to school includes Billy" would be the sentence missing a nominative pronoun, since in this case the main subject would be whoever is walking to school (the part that is left blank).
Answer: C) Billy and ____walk to school each morning.
Explanation: the nominative case in a sentence is a grammatical case for when nouns or pronouns are the subject of a verb. The nominative pronouns are I, you, he, she, it, we and they. In the given sentences, the one that is missing a nominative pronoun is option C, it should say "Billy and (nominative pronoun) walk to school each morning" for example, it could be: "Billy and I walk to school each morning"
