The idiom "keep your chin up" means to stay positive and hopeful, especially during tough or disappointing times.
- It does not mean to be proud and arrogant (A).
- It is different from being ready to fight (B) or focused on winning (D).
- The correct meaning is to remain cheerful or optimistic even after setbacks.
Answer: \(\boxed{\text{Remain cheerful in a difficult situation}}\)