A feather in one's cap means an achievement to be proud of. 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 feather in one's cap can refer to an achievement to be proud of.
• Story example: A writer may use A feather in one's cap when describing an achievement to be proud of.
• Exam example: When a sentence contains A feather in one's cap, choose the meaning “an achievement to be proud of.”