Final answer:
At level 15, barbarians in Dungeons & Dragons 5th Edition gain Persistent Rage, which prevents rage from ending early, and Intimidating Presence, enabling them to frighten adversaries.
Step-by-step explanation:
In the Advanced Placement (AP) version of Dungeons & Dragons (5th Edition), a barbarian at level 15 gains the ability of Persistent Rage and Intimidating Presence.
Persistent Rage ensures that the barbarian's rage is maintained unless they are knocked unconscious or they choose to end it. It prevents the rage from ending early due to not attacking a hostile creature or not taking damage during a turn. Intimidating Presence allows the barbarian to use an action to frighten someone with their menacing presence.
The correct answer to the question is thus C) Persistent Rage and Intimidating Presence.