省略to的不定式结构做宾补make/ see/ hear/watch sb. do等变成被动语态时，需要把to还原出来，变成sb. be made/ be seen/ be heard/ be watched to do.
His workers were made to work for twelve hours a day.（make sb. do在被动语态中变为sb. be made to do）
语态有两种：主动语态和被动语态。如果主语是动作的执行者，或者是说动作是由主语完成的，要用主动语态，如：We speak Chinese in China.在中国我们说汉语。
如果主语是动作的承受者，或者是说动作不是由主语而是由其他人完成的，则用被动语态，如：Chinese is spoken by us in China.在中国汉语被我们说。
扩展资料
被动语态应注意问题：
1、不及物动词无被动语态。
What will happen in 100 years./The dinosaurs disappeared about65 million years ago.
2、有些动词用主动形式表示被动意义。
This pen writes well. /This new book sells well.
3、感官动词或使役动词使用省略to的动词不定式，主动语态中不带to，但变为被动语态时，须加上to.
①makesomebody do something→somebody+ be +made to do something
②seesomebody do something→somebody +be +seen to do something
③Theboss made the little boy do heavy work.→The little boy was made to doheavy work by the boss.
4、如果是接双宾语的动词改为被动语态时，直接宾语（物）作主语，那么动词后要用介词，这个介词是由与其搭配的动词决定。
①Hegave me a book.→A book was given to me by him.
②Heshowed me a ticket.→A ticket was shown to me by him.
5、一些动词短语用于被动语态时，动词短语应当看作一个整体，而不能丢掉其中的介词或副词。
We can't laugh at him. →He can't be laughed at by us.