Understanding Active and Passive Voice Transformation

The question asks us to convert a sentence from active voice to passive voice. In an active sentence, the subject performs the action. In a passive sentence, the subject receives the action, and the original subject (the doer of the action) is often mentioned using 'by'.

Analyzing the Active Sentence

The given sentence in the active voice is: "We compelled the teacher to finish the class sooner."

Let's identify the key components:

• Subject: We (the ones performing the action of compelling)
• Verb: compelled (the action performed)
• Object: the teacher (the one receiving the action of compelling)
• Infinitive phrase: to finish the class sooner (tells what the teacher was compelled to do)

The structure is Subject + Verb + Object + Infinitive.

Converting to Passive Voice

To convert an active sentence to passive voice, follow these steps:

1. Make the object of the active sentence the subject of the passive sentence.
2. Change the verb to a form of "be" + the past participle of the main verb. The tense should remain the same. The active verb is "compelled", which is in the simple past tense. The passive form for simple past is "was/were" + past participle. Since the new subject "the teacher" is singular, we use "was compelled".
3. The original subject ("We") can be included as the object of the preposition "by" ("by us"), but it is often omitted if it is clear from the context or not important.
4. The rest of the sentence, including the infinitive phrase, usually follows the passive verb.

Applying these steps:

• New subject: "The teacher"
• Passive verb: "was compelled" (simple past passive of "compelled")
• Infinitive phrase: "to finish the class sooner"
• Optional phrase for original subject: "by us"

Combining these, the passive sentence is: "The teacher was compelled to finish the class sooner." The phrase "by us" can be added at the end if needed, but the sentence is complete and grammatically correct without it.

Evaluating the Options

Let's look at the given options:

1. The teacher was compelled to finish the class sooner.

   This matches the passive sentence we constructed by following the rules. The object "the teacher" becomes the subject, and the verb "compelled" (simple past) becomes "was compelled" (simple past passive). The infinitive phrase "to finish the class sooner" follows correctly.

2. The teacher finished the class compelled by us.

   This sentence is not a direct passive transformation of the original sentence. It uses "compelled by us" as a descriptive phrase after "finished the class," rather than as the main passive verb transforming the original sentence's action.

3. Finishing the class sooner was what the teacher was compelled to do.

   This is a rephrasing of the idea using a gerund phrase ("Finishing the class sooner") as the subject, followed by a relative clause. While it conveys a similar meaning, it is not a standard passive voice transformation of the original sentence structure.

4. The teacher compelled us to finish the class sooner.

   This sentence changes the subject and object completely and keeps it in the active voice ("The teacher" is the subject, "compelled" is the verb, "us" is the object). This is not the passive voice of the original sentence.

Based on the analysis, option 1 is the correct passive voice transformation of the sentence "We compelled the teacher to finish the class sooner."

Revision Table: Active vs. Passive Voice

Additional Information on Passive Voice with Infinitives

When an active sentence contains an infinitive phrase after the verb, like "We compelled the teacher to finish...", the infinitive phrase usually remains unchanged after the passive verb.

Another common structure is when the verb is followed by an object and then an infinitive (Verb + Object + Infinitive). In the passive voice, the object becomes the subject, the verb becomes passive, and the infinitive follows the passive verb.

Example:

• Active: They asked him to leave.
• Passive: He was asked to leave (by them).

This matches the structure seen in the question: compelled + the teacher (object) + to finish (infinitive).