Question

如何把句子改成被动语态（英语）

1.They often clean their classroom after school.
2.We often used keyd for locking doors.
不仅仅要的是答案，重要的是方法！

Answer 1

their classroom are often cleaned by them after school.
keys were often used by us for locking doors.

主动句是指该句主语是谓语所表示的动作行为的发出者的句子。被动句则是指该句主语是谓语所表示的动作行为的承受者的句子。
主动句和被动句互相转换的要点是主语和宾语的转换：主动句变被动句时，将主动句的宾语变为被动句的主语，主动句原来的主语与“被”构成介宾短语作被动句的状语；被动句变主动句则恰好相反。�
（四）主动句变被动句
1.主动句变被动句第一步：要看时态，时态必须保持一致。第二步：把主动句的宾语改为被动句的主语，谓语动词由主动形式改为被动形式，主动句的主语成为介词by的宾语，放在句尾。
For example:
People keep sheep for producing wool.
Sheep _______ ______ for producing wool _______ people.
答案解析：在主动句中people 是主语，是动词keep动作的执行者，sheep就是keep的承受者。在变被动语态时，把主动句中的宾语sheep变成被动句中的主语，主动句中的主语变被动句的宾语，其前加介词by。谓语动词变过去分词。故正确答案为：are，kept，by。
2．主动句改为被动句，要注意谓语动词由主动形式变为被动形式时的各种变化，具体有以下几种变化：
一般现在时的被动语态：am/is/are + 过去分词
一般过去时的被动语态：was/were + 过去分词
现在完成时的被动语态：have/has +been + 过去分词
情态动词的被动语态 ：can/may/must/．．．+be + 过去分词
一般将来时的被动语态：will/shall +be + 过去分词
现在进行时的被动语态：am/is/are +being + 过去分词
过去进行时的被动语态：was/were +being+ 过去分词

过去完成时的被动语态：had + been+ 过去分词
接上面的：
http://www.618jyw.com/Article/ShowInfo.asp?ID=43757

Answer 2

their classroom is often cleaned by them after school.
keys were used to lock doors by us.找出动作的接受者，把它变成主语，再把动词改成被动式，方法和汉语的被动句差不多

Answer 3

their classroom are often cleaned by them after school.
keys were often used by us for locking doors.

Answer 4

passive voice is the opposition to the active voice by exchanging the position of the Subject and Object