Four girls went to school by bus every day. But one day they went to school by taxi.
On their way to school, 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."
Another girl asked, "How can we do that? If we are late, our teacher will be angry. We need to have a good excuse."
The girls thought for several minutes, then one of them said, "Let's tell him that our taxi had a flat tire (轮胎了)"
"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? You all missed the test." the teacher asked.
"Our taxi had a flat tire," the girls answered.
The teacher thought for a moment, then he said, "Sit down, one in each corner of the room." The four girls did this.
Then the teacher said, "Which tire was flat? Please write down the answer on a piece of paper."
