Last Thursday a doctor came m our school to talk about the harm of smoking. He said he wouldn't go on for too long, and we saw him take his wrest-watch off and lay it on the table. I can't remember what he said about smoking, because Bob and I had other things to think about. He fin ished when the bell rang for play-time, and the headmaster told us to go out. In the playground Bob showed me the watch. He put it on his wrist, and it looked love ly. I wished I had been the one to sit by the table. It was really a beautiful watch, gold by the look of it. The headmaster came outside then, and the doctor was with him. They walked about, looking around and talking all the time. After a while the bell rang, and we got into our lines, ready to go in. The headmaster said, 'I've got a little job for boys. This doctor, who was giving us a talk just now, has lost his watch in the playground. It happened before, he says- it just slips off his wrist. So look around for it, will you? See if you're clever enough to find it. I promise that the boy who does so will get a useful reward.' Of course, Bob was not going to miss a chance like that. He's just about the luckiest boy in the school rewards just drop into his hands. We all walked about the playground, looking here and there for the watch. And I wasn't at all surprised when Bob bent down as if he was picking something up. Then he hurried past me towards the doctor. 'Where are you going?' I called out, though I knew very well where he was going. The next minute there was Bob, all smiles, handing over the watch to the old doctor and hanging about for the reward. But the doctor did not seem at all pleased. In fact he looked quite ready to thrust (插入) a knife in Bob's heart-until the headmaster burst out laughing. Bob told me later the old man hadn't even said 'Thank you' for the watch. The thing that puzzled us most of all was that Bob didn't get any reward. When he mentioned to the headmaster about k, the old man said, 'Ah, yes, we mustn't forget that. I said ' a useful re ward' , didn't I?' Then he gave Bob a big sheet of paper and told him to write a composition on the harm of smoking. Bob says he hasn't got any idea of what to write. While the doctor was talking about the harm to smoking, the two boys were______.