A different kettle of fish means a completely different matter. 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: A different kettle of fish can refer to a completely different matter.
• Story example: A writer may use A different kettle of fish when describing a completely different matter.
• Exam example: When a sentence contains A different kettle of fish, choose the meaning “a completely different matter.”