Step 1: Understanding the Concept:
This question asks to convert a sentence from the past perfect active voice to the passive voice.
Step 2: Key Rules for Conversion:
1. Identify Subject, Verb, Object: Subject is 'He', verb is 'had written', object is 'a poem'.
2. Make Object the Subject: The object 'a poem' becomes the new subject.
3. Change Verb Form: The past perfect active verb (`had + past participle`) changes to the past perfect passive form (`had + been + past participle`).
4. Make Active Subject the Agent: The subject 'He' becomes the agent 'by him'.
Step 3: Detailed Explanation:
- Active: "He had written a poem."
- New Subject: "A poem"
- New Verb: 'had written' becomes 'had been written'.
- Agent: 'by him'.
- Passive Sentence: "A poem had been written by him."
Let's check the options:
(A) & (D) Incorrect tense ('has' is present perfect). The original is past perfect ('had').
(B) Incorrect form. The passive requires 'been'.
(C) Correct tense and form.
Step 4: Final Answer:
The correct passive voice is A poem had been written by him.