Final answer:
In Dungeons & Dragons 5th edition, a barbarian replenishes all expended uses of Rage after completing a short rest or a long rest.
Step-by-step explanation:
The question, "How does a barbarian replenish rage?" refers to game mechanics within a role-playing game, likely Dungeons & Dragons. The correct answer is: A) By taking a short rest. In the 5th edition of Dungeons & Dragons, a barbarian can regain all expended uses of Rage after completing a short rest or a long rest. It's important to note that the rules can vary between different editions or homebrew settings, but according to the official rules, the options B) Automatically at the start of each turn, C) By taking a long rest, and D) By dealing critical damage in combat are not standard ways for a barbarian to replenish Rage.