let the door be shut
The door was shut.
The door was opened by whom.
This sentence is a command, it has no subject and it cannot be changed to a passive sentence.
The door was being knocked at by some body.
Can it be changed into passive voice?
Yes, "is addressed" is in the passive voice.
To change a sentence into passive the sentence must be active. 'Shut the door please' is not an active sentence, it is an imperative sentence, it has no subject. You could write something like this - You are asked to shut the door - but this is a bit awkward.
"They were surprised by a knock at the door." is passive voice.
The door was opened by whom.
This sentence is a command, it has no subject and it cannot be changed to a passive sentence.
The door was being knocked at by some body.
This
The passive voice of ''what do you do'' is "what is done by you?"
"Your name is not known by me." is passive voice.
Passive voice
No, "He is a boy" is not in passive voice. Passive voice involves rearranging the sentence to emphasize the receiver of the action rather than the doer, which would change the sentence to something like "The boy is being called."
passive active A+
"The policeman chased after Fred" is active voice.