their / its
When pronouns are said to “agree” with their antecedent (or the noun that precedes them that they are representing), what is meant that the number agrees. What that means that if the antecedent/noun is singular, then the pronoun will be singular. If the noun is plural, then the pronoun should be, too. If the pronoun does not agree with its antecedent, then there is said to be a noun-pronoun agreement error. That said, the appropriate/agreeing pronoun for “knights” is “their” because both are plural, and the appropriate/agreeing pronoun for “army” is “its” because both are singular.
