4、由主动语态转换为被动语态的几种句型：(1)将一个句子由主动语态转换为被动语态时，可按下列步骤进行：①先将主动结构的宾语改为被动结构的主语；②再将主动语态动词改为被动语态动词；③最后在被动语态之后加介词by，并将主动结构的主语放在by之后(经常被省略)，构成介词短语；④由主动语态动词改为被动语态动词时，要注意被动语态动词中助动词be的各种形式变化，因为被动语态动词的不同人称和数是由助动词be不同的形式来表示的，如：Trees are planted every spring.(2)如果主动语态动词后又有直接宾语，又有间接宾语，一般是将间接宾语改为被动语态句中的主语，将直接宾语保留在原处。如将直接宾语改为被动语态句中的主语，将间接宾语保留在原处时，一般要在间接宾语前加介词to或 for，如：Grandma
told me an interesting story last night.→Iwas
told an interesting story last night./ An interesting story was told to me last
night. (3)主动语态中的宾语加带有宾语补足语时，改为被动语态时，就将宾语改为主语，将宾补保留在原处，而成为被动语态句中主语的补足语了。宾补可以有下列几种情况：①宾补为动词不定式，如：They asked her to sing a song.
→She was asked to
sing a song. 在动词make, see, hear, watch, notice等之后，不定式的to在主动语态里可要省略，而被动语态里不能省，如：Tom was seen to come out of the lab.②宾补为分词，如：They heard them singing at the time.→They were heard singing at that time.③宾补为形容词、副词、名词或介词短语，如：She kept me busy all the
morning. →I was kept busy all the morning.(4)如果主动语态中的谓语动词为短语动词，改为被动语态时，要注意不要遗漏短语中的介词或副词，以保持短语动词的完整性，如：She always takes good care of
the children. →The children are always taken
good care of. (5)含有情态动词的动词改为被动语态时是将情态动词后面的动词原形改为被动语态，因其前有情态动词，所以构成被动语态的助动词be就要使用原形，如：They must finish the work before Friday. →The work must be finished before Friday.(6)be going to, be to, used to, have to和had better等结构，其作用相当于情态动词或助动词，在改为被动语态时，只需将后面的动词原形改为被动语态即可，如：The are not going to put off
the football match. →The football match is not
going to be put off.