Hard and fast means fixed and not changeable. 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: Hard and fast can refer to a situation involving fixed and not changeable.
• Story example: A writer may use Hard and fast when describing a situation involving fixed and not changeable.
• Exam example: When a sentence contains Hard and fast, choose the meaning “fixed and not changeable.”