英语有两种语态， 主动语态和被动语态， 主动语态表示主语是谓语动词动作的实行者，被动语态表示主语是谓语动词动作的承受者。例如：
I have repaired the radio.
The radio has been repaired.
The students cleaned the classroom.
The classroom was cleaned by the students.
be + 过去分词
A building was damaged by the storm.
Our plate was made in China.
My bike was stolen.
常用的被动语态的时态变化如下，以 ask 为例：
现在I am asked, I am being asked, I have been asked
过去I was asked,I was being asked,I had been asked
将来I shall be asked, I shall have been asked
过去将来I shall be asked
Has your TV set been repaired?
Was the kite broken?
Has the work been done?
The letter has not been sent out.
The little boy has not been found out.
The cap has not been mended yet.
Their money has not been sent to them.
被动语态表示一种主语和谓语之间的关系，当主语是动作的承受者时， 就需要用到被动语态，汉语中所说的，“汽车被撞坏了”“钢笔被修好了” 等句子就是一种被动语态的句子，在汉语中常用“被”“由”等词来表示这种被动语态。在英语中则用动词的被动语态形式来表示。被动语态中还可用 by 短语加在句后表示被动语态中动作的发出者。也就是谓语动词动作的逻辑上的主语，被动语态常用在下列情况。
The glass was broken last night.
His bike has been stolen.
He was asked to go there once more.
The bag was put into the box.
The plan has been sent to the headmaster.
Kilinton was elected the President of U.S.A.
Five people were hurt in the explosion.
A new building was set up in a short time.
动作承受者 + be + 过去分词 + by + 动作实行者。
The picture was praised by everybody.
The classroom was cleaned by us.
The bridge was built by workers from Shanxi.
The little boy was found by the police.
1) "be + 过去分词" 并非都是被动语态，系动词 be, feel, seem,look,等词后面的过去分词已转化为形容词，作表语用，表示某种状态。
I'm interested in mathematics.
He seems unsatisfied with his work.
We are determined to catch up with the developed countries.
The song is called "Don't forget me".
The food tastes good.
It smells strange.
The stone feels very cold.
The woman's clothes sell well.
He was looked down upon because of his egoism.
The children were taken good care of in the the orphanage.