Select the most appropriate option to improve the bold part of the sentence.
The wall is decorated by posters.

Correct option is C

The correct substitution of the highlighted words is (c) decorated with posters.
Explanation: The verb decorate typically takes the preposition with to indicate the material/means used: decorate something with something. In passive constructions, by normally marks the agent, not the material. Hence, “The wall is decorated with posters” is idiomatic and precise.
Grammatical rule used:
· decorate + object + with + thing used (material/instrument).
· In the passive voice, by introduces the doer/agent (e.g., The wall was decorated by the students), while with introduces the adornment (e.g., decorated with lights).
· Example: The hall was decorated with flowers for the ceremony.
· Info booster: Similarly, prefer covered with (formal) over covered in (informal) when precision is needed in exams.