Antonym of FRIEND

Answer: Option C

Friend : a person with whom one has a bond of mutual affection, typically one exclusive of sexual or family relations.
Rival : a person or thing competing with another for the same objective or for superiority in the same field of activity.
Acquaintance : knowledge or experience of something.
Foe : an enemy or opponent.
Competitor : a person who takes part in a sporting contest.

Antonym of Friend is Foe