Cast doubt on means make something seem uncertain. 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: Cast doubt on can refer to a situation involving make something seem uncertain.
• Story example: A writer may use Cast doubt on when describing a situation involving make something seem uncertain.
• Exam example: When a sentence contains Cast doubt on, choose the meaning “make something seem uncertain.”