Transform the following sentence into active voice.
All the structures built in that area had been demolished due to encroachment.

Correct option is C

The correct active voice of the given sentence is (c).
Explain the rules of conversion:
· In passive, the object becomes the subject: Object + had been + V³ (+ by + agent).
· In active, we restore an agent/subject and use the corresponding past perfect: Subject + had + V³ + object.
· Here, “all the structures (built in that area)” is the object; changing to active gives “They had demolished all the structures (built in that area)”. The participial phrase “built in that area” correctly remains as a post-modifier of “structures.”
· Structure:
· Active voice: Subject + had + past participle + object → They had demolished all the structures …
· Passive voice: Object + had been + past participle (+ by …) → All the structures … had been demolished …
· Why other options are incorrect:
· (a) build (base form) is wrong; needs built (past participle).
· (b) Grammatically fine but wordy; inserting “that were” is unnecessary because the reduced relative “built in that area” is more concise.
· (d) Adds “by the people,” an agent not stated in the original; avoid introducing new information in strict transformations.