那就举几个例子看看吧.
(其实规则就是:在情态动词后加上be,再将谓语动词(实义动词)变成过去分词,其余就是平常的被动语态转换,即将原句中的宾语变成主语,原句中的主语加上by之后变成状语.)
1.Must
You must finish homework before supper.
改被动语态:Homework must be finished (by you) before supper.
2.Should
Parents should teach children no later than 3 years old.
改被动语态:Children should be taught by parents no later than 3 years old.
3.Have to
They have to hold a meeting in the park.
改被动语态:A meeting has to be held by them in the park.
4.Can
Lily can carry that bookshelf easily.
改被动语态:That bookshelf can easily be carried by Lily.
5.Need
Tom needs to train this dog everyday.
改被动语态:This dog needs to be trained by Tom everyday.
希望可以帮助到你理解吧...