Select the option that expresses the given sentence in active voice.
The batteries in the smoke detector have been changed.

Correct option is C

The correct active voice of the given sentence is "Someone has changed the batteries in the smoke detector."
Rules for Conversion:
· Passive Voice: Object + has/have been + past participle
· Active Voice: Subject + has/have + past participle + object
Structure:
· Passive: The batteries (object) have been changed (verb) in the smoke detector.
· Active: Someone (subject) has changed (verb) the batteries (object) in the smoke detector.
Incorrect Options:
· (a) Someone had changed – Past perfect instead of present perfect.
· (b) Someone changed – Simple past instead of present perfect.
· (d) Someone has been changing – Present perfect continuous (incorrect).