Final answer:
In French, you would use the subject pronoun Tu to address a classmate.
Step-by-step explanation:
To address a classmate in French, you would use the subject pronoun Tu. This is the informal way of addressing someone and is used when you are on friendly terms with the person you are speaking to. For example, you would say, "Comment ça va, tu?" which means "How are you doing?"
Learn more about Using subject pronouns in French