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 y ou today?" Bob 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 f ather." The next day , Bob's teacher asks Bob to make sentences with( 用 ......造句 )"I,you and he" . Bob stands up and says," l'm your mother. You're my son.He is your father." All the students in Bob's class laugh( 笑 ).