The two girls are always together. There is a great affinity between them.

Answer: Option C

Affinity : a natural liking for and understanding of someone or something.
Apathy : lack of interest, enthusiasm, or concern.
Empathy : the ability to understand and share the feelings of another.
Antipathy : a deep-seated feeling of aversion.
Sympathy : feelings of pity and sorrow for someone else's misfortune.

Antonym of Affinity is Antipathy