主动语态表示主语是动作的执行者。例如：Many people speak English.
被动语态表示主语是动作的承受者，例如：English is spoken by many people.
(1)不知道或没有必要说明动作的执行者是谁。 例如： Some new computers were stolen last night.
例如：The window was broken .（by Mike）. This book was written by him. 这本书是他写的。
例如： All the people laughed at him. → He was laughed at by all people.
They make the bikes in the factory. →The bikes are made?by them?in the factory.
1. The students _______ often _______(tell) to take care of their desks and chairs.
2. Tom ________(not have) breakfast yesterday morning.
The old man is ill. He ___________ (must send) to the hospital.
4. Vegetables,eggs and fruits___________ (sell) in this shop.
5. What ______ a knife ________ (make) of? It _______________(make) of metal and wood.
6. This kind of machine ______________(can made) by uncle Wang.
7. ______ the magazine _____________(can take) out of the library?
8. The room _____________ (clean) by me every day.
9. The stars ________________ (can see) in the daytime.
10. Some flowers __________(water) by Li Ming already.
11. These kinds of machines __________(make) in Japan.
12. Apples ________________(grow) in this farm.
13. A beautiful horse _______________(draw) by John next day.
14. Planes,cars and trains _______________ (use) by business people for travelling.
15. The cinema ________________ (bulid) in 1985.
16. The bike ____________________ (must not put) here.
17. How long _____ your uncle ________(be) in the city?
18. ______ you ________(see) the film yet?
Yes, I _______(see) it last week.
19. Uncle Wang ______________(live) here since 1980
20. Listen! Someone ______________(sing).