Rewrite the sentence in active voice.
The books exhibition had been opened by the Governor.

Correct option is A

Explanation: The past perfect passive voice "The books exhibition had been opened by the Governor" changes to the past perfect active voice, "The Governor had opened the books exhibition." This retains the temporal aspect of the action being completed before another past action or time.
Grammatical rule used: Past perfect passive is converted to past perfect active to indicate that the action was completed before another past moment.
Conversion Rule: Past perfect
Subject + had + V3 + object -> <- Object + auxiliary verb (had) + been + past participle + by + subject.
Example: The letter had been written by her. -> She had written the letter.