Step 1: Understanding the Concept:
Voice in English grammar refers to the relationship between the action of the verb and the participants (subject and object).
- Active Voice: The subject performs the action (e.g., The boy kicked the ball).
- Passive Voice: The subject receives the action (e.g., The ball was kicked by the boy).
Converting from active to passive requires moving the object to the subject position, using a "be" auxiliary verb matching the original tense, and using the past participle of the main verb.
Step 2: Detailed Explanation:
Let's analyze the relationship between options (B) and (C) to verify they are a correct conversion pair.
Breaking Down Sentence (B): "She sings a song."
- Tense: Simple Present.
- Subject: "She" (The doer).
- Verb: "sings" (The action).
- Object: "a song" (The receiver).
Converting to Passive:
1. The object "a song" becomes the new subject: A song...
2. Add the auxiliary "be" verb. Since "a song" is singular and the original tense is present, we use "is": A song is...
3. Change the main verb "sings" to its past participle "sung": A song is sung...
4. The original subject "She" becomes the object "her" preceded by "by": A song is sung by her.
This perfectly matches sentence (C).
Why other options are not the correct pair:
- (A) "The letter was written by him" is a correct passive sentence, but its active counterpart ("He wrote the letter") is not listed.
- (D) "The work completed yesterday" is grammatically incorrect in the passive. It lacks the "be" verb. It should be "The work was completed yesterday."
Step 3: Final Answer:
The sentences (B) "She sings a song" and (C) "A song is sung by her" form a perfectly matched active-passive pair in the Simple Present tense.