A tall order means a difficult task or demand. 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 tall order can refer to a difficult task or demand.
• Story example: A writer may use A tall order when describing a difficult task or demand.
• Exam example: When a sentence contains A tall order, choose the meaning “a difficult task or demand.”