Correct Answer:
C. Who was helped by the rich man?
To transform an active voice sentence into the passive voice, the object of the active sentence becomes the subject of the passive sentence, and the verb is changed to a form of 'to be' plus the past participle. The original subject often becomes part of a 'by' phrase.
- Who was helped by the rich man? is correct. In the active sentence, 'Whom' is the object. In the passive voice, this object becomes the subject 'Who', and the verb 'did help' becomes 'was helped'. The original subject 'the rich man' becomes 'by the rich man'.
- Whom was helped the rich man? is incorrect because 'Whom' is an objective pronoun and cannot be the subject of the passive sentence.
- Who did help the rich man? is incorrect because it remains in the active voice.
- By whom the rich man was helped? is grammatically awkward and less natural for a question; the subject 'who' should initiate the question.