题目

An old man was going home late one night with his horse and cart after a day’s hard work. When he was not far away from his house, the light on the cart went out. He tried but could not repair it. He was near his home, and so he went along the road without a light. When a policeman saw this, he stopped the old man.“Where is your light?” asked the policeman. “No man may take a cart along the road at night without a light. You know that. You have broken the law.” “I had a light, but it has just gone out,” said the old man. “I don’t believe that story. What’s your name and whe二元一次方程x+2y=7的正整数解有3组，分别为 ．