Dig one's heels in means refuse to change one's mind. 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: Dig one's heels in can refer to a situation involving refuse to change one's mind.
• Story example: A writer may use Dig one's heels in when describing a situation involving refuse to change one's mind.
• Exam example: When a sentence contains Dig one's heels in, choose the meaning “refuse to change one's mind.”