胡老师从河北到西藏工作，半年后体检时发现，血液中有一种成分显著增加．增加的成分最可能是（　　）

Bob Smith is a little boy. On the first day at school, his teacher, Ms. Green, teaches him three words—you, he and I. 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, Mom. I am your teacher, you are my student and he is your classmate.”His mother says,“No, dear. You are wrong.”Then she says, “I am your mother. You are my son. He is your father.”
 The next morning at school, Bob’s teacher asks Bob to make sentences with the words “you, he and I”. Bob stands up and says, “I am your mother. You are my son. He is your father.”