一、用to
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 .
例：make somebody do something→somebody+ be +made to do something
see somebody do something→somebody +be +seen to do something
A girl saw my wallet drop when she passed by.→My wallet was seen to drop by a girl when she passed by.
The boss made the little boy do heavy work.→The little boy was made to do heavy work by the boss.
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.
He gave me a book.→A book was given to me by him.
He showed me a ticket.→A ticket was shown to me by him.
My father bought me a new bike.→A new bike was bought for me by my father.
二、用by
把主动语态中的主语放在介词by之后作宾语，将主格改为宾格。
例如：All the people laughed at him.=He was laughed at by all people.
They make the bikes in the factory.=The bikes are made by them in the factory.
记忆歌诀：
宾变主，主变宾，by短语后面跟。
三、在主动语态和被动语态用法一样。
谓语动词变被动，be后“过分”来使用。
追答三、for在主动语态和被动语态用法一样。