Choose the option in which VOICE in the given sentence has been changed correctly.
Who is knocking at the door?

Correct option is A

The correct passive voice of the sentence “Who is knocking at the door?” is (a) By whom is the door being knocked at?
Detailed Explanation (English):
· Active voice: Who is knocking at the door?
· Subject: Who
· Verb: is knocking
· Object: the door
· Passive voice structure for present continuous: is/am/are + being + past participle (V³)
· The question word who changes to by whom in the passive voice.
Therefore: By whom is the door being knocked at?
Grammatical rule used:
When changing an interrogative sentence from active to passive,
1. The helping verb comes before the subject.
2. “Who” becomes “by whom.”
3. The tense remains the same (here, present continuous → is being + V³).
Explanation of the grammatical rule in Hindi:
जब किसी प्रश्नवाचक वाक्य (interrogative sentence) को active से passive में बदला जाता है—
· “Who” को “By whom” में बदला जाता है।
· वाक्य में “is/am/are + being + V³” संरचना प्रयोग होती है।
· सहायक क्रिया (helping verb) विषय (subject) के पहले आती है।
Example:
· Active: Who is painting the wall?
· Passive: By whom is the wall being painted?