教室被学生们打扫了。

被动语态的构成：

be+过去分词

A building was damaged by the storm.

暴风雨毁坏了一座建筑物。

Our plate was made in China.

我们的盘子是中国生产的。

My bike was stolen.

我的自行车被盗了。

常用的被动语态的时态变化如下，以ask为例：

一般进行完成

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

被动语态的疑问句是把助动词提前到句首。

Has your TV set been repaired?

你的电视机修了吗?

Was the kite broken?

风筝破了吗?

Has the work been done?

工作结束了吗?

被动语态的否定式是在助动词后面加not.

The letter has not been sent out.

信还没有发出去。

The little boy has not been found out.

小孩还没有找到。

The cap has not been mended yet.

帽子还没有补好。

Their money has not been sent to them.

他们的钱还没有送到他们手中。

三、英语六级语法常考知识点：suggest

1)It is demanded/necessary/a pity+that…结构中的主语从句的谓语动词要用should加动词原形，should可省略。

句型：

(1)suggested

It is(2)important　that…+(should)do

(3)a pity

(1)suggested,ordered,proposed,required,demanded,requested,insisted;+(should)do

(2)important,necessary,natural,strange

a pity,a shame,no wonder