情态动词的被动语态结构为"情态动词 + be + 过去分词"。
要点讲解
- 结构：can/may/must/should/need + be + 过去分词。
- can be done 能被做：This book can be found in the library. 这本书能在图书馆找到。
- must be done 必须被做：The work must be done at once. 这工作必须马上做。
- should be done 应该被做：The young should be cared for. 年轻人应该得到关爱。
- may be done 可能被做：The problem may be solved soon. 这个问题可能很快解决。
- need 的被动：The room needs cleaning. = The room needs to be cleaned. 房间需要打扫。
- 注意区别：must be done（必须被做）与 must have been done（过去一定被做了）。
经典例句
- Trees should be planted in spring.
树应该在春天种植。 - The classroom must be kept clean.
教室必须保持干净。 - This work can be finished in two hours.
这项工作能在两小时内完成。
易错提醒
- need doing = need to be done（主动形式表被动含义），如 The car needs washing. 车需要清洗了。