Keep the ball rolling means keep an activity or discussion continuing. This answer is correct because the expression has a fixed figurative meaning in English. In an SSC idiom question, students should match the whole phrase with its accepted meaning rather than translate each word separately.

• Classroom example: Keep the ball rolling can refer to a situation involving keep an activity or discussion continuing.
• Story example: A writer may use Keep the ball rolling when describing a situation involving keep an activity or discussion continuing.
• Exam example: When a sentence contains Keep the ball rolling, choose the meaning “keep an activity or discussion continuing.”