把主动语态改成被动语态.1.We have already finished the experiment.2.At this time yesterday ,they were cleaning their house .3.Mr.Li me to listen the tape carefully every day .4.He will send the letter to Mary tomorrow.5.Chinese people built The Great Wall many years ago.3.Mr.Li told me to listen the tape carefully every day .

The experiment has already been finished.
At this time yesterday，their house was being cleaned.
I am let .....
总之就是把后面的宾语换成主语，再用be done 的形式换上。。。

The experiment have already been finished by us
At this time yesterday , their house were being cleaning by them .
第三句是不是有个ask？
i am asked to listen the tape carefully by Mr.Li every day .
the letter wil been sent to Mary by me tomorrow.
The Great Wall was built by chinese people many years ago.

The experiment has already been finished by us.
.At this time yesterday ,their house were being cleaned by them.
The tape is listened carefully every day by Mr.Li
The letter will be sent to Mary tomorrow by him.
The Great Wall was built by Chinese people many years ago.