Concept:A sentence is in active voice when the subject performs the action. It is in passive voice when the subject receives the action.
Explanation:Look for a sentence where the subject is not doing the action but is being acted upon.
Option C: "A letter was written by him yesterday." Here, the subject "a letter" is receiving the action of writing. The doer (him) appears after "by". This is passive voice.
Check the others:
Option A: "My nerves are bad tonight." — no action, just a state.
Option B: "He takes his classes punctually." — subject "he" performs the action (active).
Option D: "It looks good and sizzling." — subject "it" describes a state, not an action.
Only option C has the structure: object + verb (was written) + by + doer.
Answer:A letter was written by him yesterday (Option C).