The sentence "The book contains useful information." is in the active voice.

Passive voice:
Useful information is contained in the book.

Explanation:
The object "useful information" becomes the subject in the passive voice.

The verb "contains" (present simple) changes to "is contained" in passive form.

The sentence "Please keep off the green." is in the active voice and imperative form.

Passive voice:
You are requested to keep off the green.

Explanation:
Imperative sentences in passive voice are often changed using structures like "You are requested to...", "You are advised to...", or "Let..." depending on the tone.

"Keep off the green" means "do not step on the grass," and in passive, we use "You are requested to..." to keep the politeness and intent.

The sentence "One should take care of one's health." is in the active voice.

Passive voice:
One's health should be taken care of.

Explanation:
The object "one's health" becomes the subject in the passive voice.

The modal verb "should" is followed by "be + past participle" (i.e., "be taken care of").

Let us finish the game

Change the voice. (Passive) = Let the voice be changed.

Scarcely had I reached the station when he left.

I shall go to the cinema after I complete my work.

The teacher asked Kamal why he was talking in the class and warned that he should behave himself.

The Brigadier ordered the soldiers to march on.

Ismail told me that as soon as I had gone out he had come.

He told me that happiness consists in contentment.

I was personally known to him.

I asked you what you had thought of me.

I told him that if I had been him I should have waited.

He wished that he had had wings of dove.