A pipe dream means an unrealistic hope or plan. 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 pipe dream can refer to an unrealistic hope or plan.
• Story example: A writer may use A pipe dream when describing an unrealistic hope or plan.
• Exam example: When a sentence contains A pipe dream, choose the meaning “an unrealistic hope or plan.”