将下列句子改为被动语态。
We must speak to the old people politely.
Must the old people _______  _______  to politely?
Dad cleaned the car yesterday.
The car ______  _________ by Dad yesterday.
We often water these young trees
These young trees ______ often _______  by us.
The boy broke the window yesterday.
The window ________  ________ by the boy yesterday.
I will give him a camera as a present.
A camera _______  ________ _________ to him by me as a present.