Final answer:
At level 17, barbarians in Dungeons & Dragons gain 'Persistent Rage' and 'Brutal Critical', which enhance their rage duration and damage output on critical hits.
Step-by-step explanation:
In Dungeons & Dragons, which is the subject of the question, barbarians at level 17 gain certain class-specific abilities. The correct answer is D) Persistent Rage and Brutal Critical. Persistent Rage means that the barbarian's rage is no longer limited by its usual duration, so it doesn't end early unless the barbarian falls unconscious or chooses to end it.
On the other hand, Brutal Critical allows the barbarian to roll additional damage dice when scoring a critical hit, increasing the damage output significantly during combat.
These abilities enhance the barbarian's staying power and damage potential in battle, respectively.