1）can/could+be+动词过去分词，表示“可以被……”“可能被……”“应该被……”“必须被……”等
除了can/could，还可以用情态动词may/might;must/have to;should/ought to;had better/would rather;use to/would等
需要注意：need+doing直接表示“需要被……”
2）和情态动词结合的形式：
The food could be taken away.
食品可以被带走
The food might be taken away.
食品可能被带走
The food must be taken away.
食品必须被带走
The food should be taken away.
食品应该被带走
The food needs taking away.
食品需要被带走
The food had better be taken away.
食品最好被带走
Books used to be returned in two days.
书本过去常常在2天之内被还回去
每日一句：Doubt is the key to knowledge.怀疑是知识的钥匙
