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?”
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?”

Student ：“A hundred and twenty millions.”
学生：“1.2亿根。”

Teacher：“How do you know it?”
老师：“你怎么知道?”

Student：“It is not necessary to answer the second question.”
学生：“第二题不需回答。”