Answer:
C. Their
Step-by-step explanation:
Pronouns are words we use instead of nouns or noun phrases. The antecedent of a pronoun is the word it refers to. For example, in the sentence John lost his keys, the antecedent of the pronoun his is John. We used this pronoun instead of repeating John's name.
The possessive pronoun that should be used in the given sentence is their. Its antecedent is the same as the one of the pronoun everyone. Everyone is an indefinite pronoun, and in the given context, it's used to refer to every person in the narrator's group. This group probably consists of both men and women, which is another reason the pronoun their should be used.