They speak English.他们讲英语。
主语“他们”是“讲”这一行为的执行者，是主动句，动词用主动语态来表示； English is spoken by them.英语由他们讲。
He opened the door.他打开了这扇门。（主动语态）
The door was opened.这扇门被打开了。（被动语态）
Tom killed him. → He was killed by Tom.
They held a meeting yesterday. → A meeting was held by them yesterday.
He sang a song. → A song was sung by him.
含有双宾语，即直接宾语（常指事物）和间接宾语（常指人）的句子，每个宾语都可变为被动语态的主语，即其被动语态有两种形式。但多以间接宾语作主语。 Jack told us the truth.杰克告诉了我们真相。
We were told the truth by Jack.
The truth was told (to) us by Jack.
1、 一般现在时：am/is/are +过去分词
We are taught English by her.由她教我们英语。
A present was given to me by Mary.玛丽给了我一件礼物。
3、 一般将来时：will be+过去分词
The desk will be mended by him.这张桌子将由他修理。
4、 现在进行时：am/is/are +being + 过去分词
The walls are being painted now.正在粉刷墙壁。
5、 过去进行时：was/were +being + 过去分词
The talk was being given at this time yesterday.昨天这个时候正在作报告。
6、 现在完成时：have/has been+过去分词
The flowers have been watered.这些花已经被浇了。
7、 过去完成时：had been+过去分词
She said this lift had never been used.
8、 过去将来时：would be+过去分词
The film would be shown again sometime next week.
Tables can be made of stone.桌子可由石头制造。
Tables could be made of stone at that time. 那时桌子可由石头制造。（一般过去时） Can tables be made of stone? 桌子能用石头制造吗？（疑问句）
Appear, rise, die, happen, occur, lie, depart, belong to, break out, take place等不及物动词不能用于被动语态。
常见的有：hold, have, cost, contain, become, ail, look like等
The meat is cooking.肉在煮着。
The cakes are baking,蛋糕在烘。
The book is printing.这本书正在印刷。
1）某些感官动词和系动词接形容词可以表示被动意义。如：look, smell, taste, feel, prove, wear, sound等
Her bedroom looks very clean and tidy.她的卧室看起来非常干净和整洁。
2）动名词的主动形式表示被动语态。如：want, deserve, need, require, take, worth等 The book is worth reading.这本书值得一读。
The children need looking after.孩子们需要照看。
The conversation is hard to understand.对这话很难理解。
The fish is not easy to fish.鱼不容易钓。The passage is difficult to read.这段文章很难读懂。
1.带双宾语句子的被动语态.一般把间接宾语变为被动语态的主语，则另一个不动。如把直接宾语变为被动语态的主语则需在间宾前加 for 或 to 如：1.He gave me a book.
－I was given a book by him.
－A book was given to me by Tom.
2. I bought him a book.
－He was bought a book by me.
－A book was buoght for him by me.
1、They take good care of my child.
-----My child is taken good care of .
2、I turned off the radio.
---The radio was turned off (by me).
3.在主动语态中省去to 在变为被动语态时应补出来即hear , watch , see , make , let ,这些词在变被动句时必须加to.
1.I saw him play basketball last Sunday.
Hewas seento play basketball last Sunday.
2.The boss makes him work for 10 hours.
He is madeto work for 10 hours.