Final answer:
A barbarian's Unarmored Defense ability adds their Constitution and Dexterity modifiers to their AC when not wearing armor, reflecting their inherent resilience.
Step-by-step explanation:
The barbarian's Unarmored Defense ability in the context of role-playing games, specifically Dungeons & Dragons, allows a barbarian character to gain a bonus to their Armor Class (AC) when they are not wearing any armor. The correct answer to the question is C) Barbarians add their Constitution and Dexterity modifiers to their AC when not wearing armor. This reflects the barbarian's natural resilience and agility, providing them with a defensive bonus even without the protection of armor. This feature encourages a barbarian to rely on their inherent toughness and quickness in battle.