Teacher:" I have two questions, it isn't necessary to answer the second question if you know the result of the first question.How much hair do you have?"

　　Student： " A hundred and twenty millions."

　　Teacher:" How do you know it?"

　　Student:" It is not necessary to answer the second question."

　　老师："我有两个题目，你若能答出第一题就不需答第二题。你有多少根头发?"

　　学生："1.2亿根。"

　　老师："你怎么知道?"

　　学生："第二题不需回答。"