Final answer:
A barbarian's rage damage in Dungeons & Dragons increases at even-numbered levels, specifically at levels 2, 4, 8, 12, 16, and 20.
Step-by-step explanation:
The question is asking about the progression of a barbarian's rage damage in the game of Dungeons & Dragons, which is detailed in the class's feature description. The correct answer to the question "What levels increase a barbarian's rage damage?" is C) Even-numbered levels. In the Dungeons & Dragons 5th Edition Player's Handbook, a barbarian's rage damage increases at 2nd level and then again at every other level after that, which are the 4th, 8th, 12th, 16th, and 20th levels. In Dungeons and Dragons, a barbarian's rage damage increases at levels 9, 16, and 20. At these levels, a barbarian gains additional damage to their melee weapon attacks while raging.