五、含有情态动词的被动语态

　　含有情态动词的主动句变成被动句时，由“情态动词+be+过去分词”构成，原来带to的情态动词变成被动语态后“to”仍要保留。

　　记忆歌诀：情态动词变动，情态加be加“过分”，原来带to要保留。例如：

　　1) We can repair this watch in two days. = This watch can be repaired in two days.

　　2) You ought to take it away. = It ought to be taken away.

　　3) They should do it at once. = It should be done at once