根据短文理解选择答案。

    Bob is six years old. He is old enough to go to school. On the first day, his teacher teaches him three words, “I, you, he”. Then the teacher says, “I am your teacher. You are my student. He is your classmate.” When school is over, Bob goes home. His mother asks him, “What does your teacher teach you today?” Bob says with a smile, “Listen, Mum and Dad, I am your teacher. You are my student. He is your classmate. His mother says, “No, dear. You're wrong.” Then she says, I am your mother. You're my son. He's your father. ” The next day, Bob's teacher asks Bob to make sentences with(用……造句）“I, you and he”.

     Bob stands up and says, “I'm your mother. You're my son. He is your father.” All the students in Bob's class laugh (笑).