英语基本句型中，只有 S+V+O, S+V+O+Co, S+V+Oi+Od, 三种句型可转换成被动形
式。
1． S + V + O 转换成被动形式：
　a. 将主动结构中的宾语变为被动结构中的主语；谓语动词变为被动语态；然后在谓
　　语动词的被动语态后加 by，再将主动结构中的主语置于介词 by 之后（若为人称代
　　词，须将其主格变为宾格；若被动结构中的 by 短语没必要指出，则可省去），如：
　　　The teacher has not correct the homework.
　　　→The homework has not been corrected by the teacher.
　　　I wrote that letter last night.
　　　→That letter was written (by me) last night.

　b. 如果宾语是 that 从句，变为被动形式时可用 it 作被动句的形式主语，或把主动
　　句中宾语从句的主语变为被动句的主语，宾语从句中的谓语部分变为不定式短语，
　　如：
　　　They know that he is a famous scientist.
　　　→It is known that he is a famous scientist.
　　　→He is known to be a famous scientist.

2． S + V + O + Co 转换成被动形式：将主动结构中的宾语变为被动结构中的主语，
　　宾补不变；如果宾补是不带 to 的不定式，变为被动形式时，作为主补的不定式必须带 to，
　　如：
　　　They elected her chairman of the club.
　　　→She was elected chairman of the club.
　　　The boss made the secretary (to) work overtime
　　　→The secretary was made to work overtime.

3． S + V + Oi + Od 转换成被动形式：将主动结构中的一个宾语变为被动结构中的主语，
　　另一宾语不变，如果将主动结构中的直接宾语变为被动结构中的的主语，间接宾语前则
　　加介词 to（可省）或 for（一般不可省），如：
　　　My sister gave me a new dress.
　　　I was given a new dress.
　　　A new dress was given to me.