Final answer:
The central theme of O. Henry's "After Twenty Years" is the importance of relying on knowledge and training rather than giving in to fear.
Step-by-step explanation:
The central theme of O. Henry's "After Twenty Years" is the importance of relying on knowledge and training rather than giving in to fear. The story depicts two friends who had made a pact to meet after twenty years, but one of them is now a police officer who is duty-bound to arrest the other for a past crime.
The theme is revealed through the dialogue and actions of the characters, emphasizing the message that it is crucial to stick to one's principles and trust in one's abilities.