Final answer:
At level 7, barbarians gain the abilities Feral Instinct and Mindless Rage, which enhance their initiative and protect them from certain mental effects during combat.
Step-by-step explanation:
The abilities barbarians gain at level 7 are Feral Instinct and Mindless Rage. The Feral Instinct ability improves the barbarian's initiative, allowing them to act faster in combat by granting them advantage on initiative rolls. Additionally, this ability allows the barbarian to not be surprised as long as they aren't incapacitated when they enter battle.
Mindless Rage provides an improvement to the barbarian's existing Rage feature, preventing them from being charmed or frightened while raging. Therefore, the correct answer to the question is B) Feral Instinct and Mindless Rage.