A medical student was called on to state how much of a certain drug he would give to a patient. He promptly replied: "Five grains." 　A minute later the student asked the professor, "May I correct my answer?" The professor looked at his watch and said: "It's too late. Your patient died thirty seconds ago." 　一个医科学生被要求说明他给病人服的那种药的用量。他立即回答道：“五粒。” 一分钟后，这个学生问教授：“我可以改正我的回答吗？”教授看看手表，说：“太晚啦，你的病人已在30秒钟以前死了。”