At one time Einstein traveled all over the United States giving lectures. He traveled by car and soon became quite friendly with the driver.
The driver always listened to Einstein,s lecture, which the great scien tist made again and again. One day, he told einstein he knew the lecture so well that he could talk next time？ Einstein agreed.
That evening both of them went along to the lecture hall. nobody there had seen Einstein before. As the driver took his place on the stage （讲台）,everybody clapped （鼓掌）. Then he began the lecture, while Einstein sat quietly a few steps behind.
After a short lecture, a man stopped them and asked the driver a very difficult question. The driver listened carefully. Certainly he did not under stand a thing but he nodded his head as if he did and said that such question was very interesting but really quite simple. In fact, in order to show how simple it really was, he would ask his driver to answer it.