In the following question, a sentence has been given in the active voice (interrogative in the present perfect). Out of the four alternatives suggested, select the one which best expresses the same sentence in the passive voice. Who has destroyed Nagasaki?

Introduction / Context:
This question checks your ability to convert an interrogative sentence in the present perfect tense from active voice to passive voice. The sentence is "Who has destroyed Nagasaki?" It uses the interrogative pronoun "who" and the auxiliary "has" with the past participle "destroyed." The passive version must preserve both the tense and the question form while shifting the focus to Nagasaki as the grammatical subject.

Given Data / Assumptions:

• Active sentence: Who has destroyed Nagasaki?
• Subject in active voice: who (unknown doer).
• Object: Nagasaki.
• Tense: present perfect (has destroyed).
• We must transform this into a passive question with correct auxiliary placement.

Concept / Approach:
To change such a question into passive voice, we make the object "Nagasaki" the subject of the sentence, introduce the agent with "by whom," and keep the present perfect structure as "has been destroyed." In a passive question starting with a question phrase, the auxiliary "has" must come before the subject "Nagasaki." Therefore, the correct pattern is "By whom has Nagasaki been destroyed?" which is both grammatically correct and faithful to the meaning of the original.

Step-by-Step Solution:
Step 1: Move the object "Nagasaki" into subject position in the passive sentence.Step 2: Form the passive present perfect: has been destroyed.Step 3: Replace "who" with "by whom" to introduce the doer in passive voice.Step 4: Use the correct question word order: auxiliary "has" before subject "Nagasaki."Step 5: Combine these elements to get the full question: By whom has Nagasaki been destroyed.

Verification / Alternative check:
If we attempt to convert "By whom has Nagasaki been destroyed?" back into active voice, we replace "by whom" with "who" and change "has been destroyed" to "has destroyed," keeping Nagasaki as the object. This gives "Who has destroyed Nagasaki?" which is the original sentence. This back conversion confirms that the tense, meaning, and interrogative structure have been preserved correctly.

Why Other Options Are Wrong:
"By whom Nagasaki have been destroyed?" uses "have" instead of "has," which is incorrect because Nagasaki is singular. "By whom Nagasaki had been destroyed?" changes the tense to past perfect, which does not match the original present perfect. "By whom Nagasaki has been destroyed?" lacks proper question inversion, because in English questions the auxiliary should come before the subject. "Who has Nagasaki been destroyed by?" is more informal and has a preposition at the end; exams normally prefer the more formal "By whom has Nagasaki been destroyed?" pattern.

Common Pitfalls:
Students often forget to maintain the exact tense when changing from active to passive and may switch to past perfect or simple past by mistake. Another common error is incorrect auxiliary agreement, such as using "have" with a singular subject. There is also a tendency to ignore English question word order and leave the auxiliary after the subject. To avoid these issues, remember that present perfect passive is formed with "has been" or "have been" plus past participle and that in questions, the auxiliary must appear before the subject.

Final Answer:
By whom has Nagasaki been destroyed?