Answer:
B Their
Step-by-step explanation:
A pronoun is word that can be used in place of noun or noun phrase.
Some of the more commonly used types of pronouns are;
Personal Subject Pronouns: I, we, you, he/she, they, it.
Personal Object Pronouns: me, us, them, him/her it
Possessive Pronouns: My, our, your, his/her, their, its.
First option (us) is a personal object pronoun.
Third option (would) is not a pronoun, it is a helping verb.
Fourth option (they) is a personal subject pronoun.