主动变被动
宾变主、主变 by 短语、谓语变 be done。
They built it. → It was built by them.
要点
- 把主动句的宾语提到前面作主语。
- 把谓语动词改成「be + 过去分词」，be 的时态跟原句一致。
- 原主语变成 by 短语，常可省略。
- by 短语里的人称代词要用宾格。
- 疑问句改被动时那根 do 是被 be 顶掉的：Did they take the letters away? → Were the letters taken away? —— 别写成 Did the letters be taken away?，助动词那一格只能留给 be。
- 短语动词整体搬过去，后面的介词或副词一个都不能掉：They sent for the doctor → The doctor was sent for. ／ They laughed at him → He was laughed at —— 掉一个介词，意思就不是那件事。
- "人们说…"这类无人称主动能整体收成"主语 + is said to…"：People say the bridge is unsafe → The bridge is said to be unsafe. —— 比硬挂一个 by people 干净，也是书面里最常见的被动。
例句
It was invented by Edison.
它是爱迪生发明的。
The phone was invented by Bell.
电话是贝尔发明的。
Kites were invented by Chinese people.
风筝是中国人发明的。
Who was the zipper invented by?
拉链是谁发明的？
His grandmother is looked after by the whole family.
他祖母由全家人照顾。
The old town is said to be the poet's birthplace.
据说这座古镇就是那位诗人的出生地。
易错提示
- 变被动时别丢了时态：built 要变成 was built。
- 不知道执行者或不必说出时，by 短语直接省掉。
- 改完先查主谓是否还一致：原来当宾语的那块现在是主语，be 就得跟着它的单复数走 —— The books were bought（不写 was bought）。
- 问"谁做的"时介词留在句末：Who was the zipper invented by? —— 改成 By whom… 开头只算极正式的书面写法，日常不必这么改。