You were asked to determine if the following sentence uses pronoun-antecedent agreement:
Damien is running for class president, and his sister is helping them with the campaign.
Remember, for a pronoun and its antecedent to agree, they must have the same gender and number. The gender of words can be female, male, or neutral. The number is either singular or plural.
If an antecedent is neutral and refers to a person or animal, it can be used with a male or female pronoun based on the other information in the sentence. However, inanimate objects do not have gender, so they are always renamed with neutral pronouns.
Take a look at the following sentence that includes both a pronoun and its antecedent:
Jennifer always makes the dessert because she is the best baker.
The pronoun she agrees with its antecedent Jennifer (the noun it renames). Both words are singular in number and female in gender. This is what you look for when checking for pronoun-antecedent agreement.