Keep one's nose clean means avoid trouble or wrongdoing. 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 one's nose clean can refer to a situation involving avoid trouble or wrongdoing.
• Story example: A writer may use Keep one's nose clean when describing a situation involving avoid trouble or wrongdoing.
• Exam example: When a sentence contains Keep one's nose clean, choose the meaning “avoid trouble or wrongdoing.”