Four girls went to school every day by taxi.
  One day one of the girls said, “There’s a test this morning.
Let’s get to school late. Then we won’t have to take the test.”
  “What can we tell the teacher?” one of the girls said. “He’ll
be angry. We’ll need a good excuse.”
  The girls thought for several moments, and then one of
them said, “Let’s tell him that our taxi had a flat tire.”
  “That’s a good idea,” the other girls said. “We’ll tell him
that.”
They arrived at school an hour later. The test was finished.
  “Why are you late?” the teacher asked. “You missed the
test.”
  “Our taxi had a flat tire,” one of the girls said.
   The teacher thought for a moment, and then he said, “Sit
down, one of you in each corner of the room.”

  The four girls did this.
  Then the teacher said, “Write the answer to this question
on a piece of paper: Which tire was flat?”

                一个难题
  有四个女孩每天都坐出租车去上学。
  一天，一个女孩说：“今天早晨有考试，我们晚些去学校，那样就不用
考试啦。”
  “可怎么跟老师解释呢？” 另一个女孩说，“他会生气的，咱们得找个
合理的借口。”
  女孩们想了一会儿，其中一个说：“那我们就告诉老师，乘坐的出租车
轮胎爆胎了。”
  “好主意！” 其他女孩说，“我们就这么说。”
结果她们迟到了一个小时。显然，考试已经结束了。
  “你们为什么迟到呢？”老师问，“你们已经错过了考试。”
  “我们乘坐的出租车爆胎了，”其中一个女孩说。
  老师想了一会儿，说：“你们四人各坐到教室的一个角落去。”
四个女孩照做了。
  接着，老师说： “在纸上回答一个问题：是哪个轮胎爆了？”