The window is opened by someone every day.
Chocolate was bought for me by my grandfather many years ago.或
I was bought chocolate by my grandfather many years ago.
Lunch has been eaten by li ming.
The watch can be repaired by us.
A meal has been prepared for you by someone.
A letter must be sent to him by someone.
在被动语态 中我们往往省略by和后面的部分,