A pronoun and its antecedent must agree in

A pronoun and its antecedent must always agree in number; whether it is singular or plural. If the antecedent used is singular, then your pronoun should be singular too. If the antecedent is in plural form, the pronoun you use should also be in plural form. For example:

-The girls made themselves some sandwiches.

In this example, the antecedent used is "girls" which is in the plural form; therefore, the pronoun should agree to the antecedent and use the word "themselves".