Final answer:
Peter, Peter, and Cris are a compound subject in the sentence, as they are joined by the conjunction 'and' and share the same verb.
Step-by-step explanation:
In answer to the student's question, Peter, Peter, and Cris are a compound subject in the sentence provided. A compound subject consists of two or more subjects that are joined by a conjunction such as 'and,' and they share the same verb. This can be seen in sentences like 'Antonio and I share an apartment,' where 'Antonio and I' act together as the subject of the sentence.
In terms of pronoun case, subjective case pronouns function as subjects, like 'I' in 'Antonio and I,' whereas objective case pronouns function as objects, like 'me' in 'disagreements about the dishes come up between Antonio and me.' When determining whether a group of words is a compound subject, it's crucial to identify if they are joined by a conjunction like 'and' and act together as the main actors doing the verb in the sentence.