Select the most appropriate meaning of the given idiom.
A hard nut to crack

Correct option is D

The idiom "A hard nut to crack" means a difficult person or a difficult problem/situation to deal with.
Explanation and Usage: This idiom is used to describe someone or something that is particularly challenging or difficult to understand, solve, or deal with. It often refers to a person who is stubborn, uncooperative, or tough to influence.
Example:
· The new manager is a hard nut to crack; he doesn't share his thoughts easily.