Select the most appropriate option to fill in the blank.
The workers agitated ________ better working conditions.

Correct option is C

The correct option to fill in the blank is (c) for.
Workers agitate for something when they demand or press for it; the verb–preposition collocation is fixed in standard usage. Hence, “agitated for better working conditions” is idiomatic and precise. (Hindi: agitate for = किसी बात के लिए आन्दोलन करना/मांग उठाना)
Example: The union agitated for safer machinery and fair wages.
Why other options are incorrect:
• at — location-focused preposition; doesn’t collocate with agitate in this sense. (Hindi: पर)
• by — indicates agency/instrument; wrong with the sense “demand.” (Hindi: द्वारा)
• to — marks direction/infinitive; not used after agitate for object of demand. (Hindi: को)