David is six years old. He is oldenoughto go to school. On Monday morning, 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, David goes home. His mother asks him, "What does your teacher teach you today?" David says with a smile, "Listen, Mum. 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, David's teacher asks David to make sentences with "I, you and he".

    David stands up and says, "I'm your mother. You're my son. He is your father." All the students in David's class laugh (发笑).