An axe to grind means a private reason for being involved, often selfish. 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: An axe to grind can refer to a private reason for being involved, often selfish.
• Story example: A writer may use An axe to grind when describing a private reason for being involved, often selfish.
• Exam example: When a sentence contains An axe to grind, choose the meaning “a private reason for being involved, often selfish.”