An eye-opener means something that makes someone understand the truth. 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 eye-opener can refer to a situation involving something that makes someone understand the truth.
• Story example: A writer may use An eye-opener when describing a situation involving something that makes someone understand the truth.
• Exam example: When a sentence contains An eye-opener, choose the meaning “something that makes someone understand the truth.”