Select the option that expresses the given sentence in passive voice.
They built a new house last year.

Correct option is C

The correct passive voice of the given sentence is (c).
When converting an active voice sentence to passive voice, several key changes are made to the sentence structure, specifically with the verb form and the placement of the subject and object. Let's go over the rules applied here:
Rules of Conversion for Active to Passive Voice:
1. Identify the Subject, Verb, and Object:
· In the active sentence, “They built a new house last year,” the subject is “They,” the verb is “built,” and the object is “a new house.”
2. Switch the Position of the Subject and Object:
· In passive voice, the object of the active sentence becomes the subject of the passive sentence, and the original subject becomes the agent, introduced by “by.”
· So, “a new house” becomes the subject, and “they” is introduced with “by.”
3. Change the Verb Form to Passive:
· In passive voice, the main verb is changed to a passive form, typically by using a form of “to be” with the past participle of the main verb.
· Here, “built” is the past simple form of the verb. In passive voice, “was” (past simple of “to be”) is used with “built” (the past participle of the main verb).
· Thus, “built” in active voice becomes “was built” in passive voice.
4. Maintain the Tense:
· The tense of the verb in the active sentence is simple past, which must remain in simple past in passive voice.
· Therefore, “built” becomes “was built.”
5. Time Expressions Remain Unchanged:
· Time expressions like “last year” remain at the end of the sentence and do not impact the voice conversion.
Applied Example:
· Active Voice: They built a new house last year.
· Passive Voice: A new house was built by them last year.
Why Other Options Are Incorrect:
· (a): “A new house was being built by them last year.”
· This option incorrectly uses the past continuous tense (“was being built”) rather than the simple past.
· (b): “They had been building a new house last year.”
· This option is not in passive voice; it’s a past perfect continuous sentence in active voice.
· (d): “A new house is being built by them last year.”
· This option incorrectly uses the present continuous tense (“is being built”) instead of the simple past tense.