A doctor had a son. He also became a doctor after graduation, and joined his father in his clinic(诊所).
　　Before long his father decided to have a holiday, and he left his son to look after all his patients.
　　When he returned from holidays he asked his son if anything had happened. “Well, yes, Dad”, the son said, feeling very proud of himself, “Do you remember Mrs. Jones? You have treated(治疗)her back pains for twenty years. Well, they are gone now. Do you know who did it? Your son, I did it.” “I see,” replied his father, not very pleased, “Mrs. Jones’s back paid for your university fees I was hoping they would pay for your new car, too.”