Gain ground means become more accepted or successful. 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: Gain ground can refer to a situation involving become more accepted or successful.
• Story example: A writer may use Gain ground when describing a situation involving become more accepted or successful.
• Exam example: When a sentence contains Gain ground, choose the meaning “become more accepted or successful.”