Answer: Join
Explanation: Joins is grammatically incorrect
There are a couple of pronouns in this sentence - she, us, both, and your. However, only one of these is a third person personal pronoun, and that is she.
Us is first person plural, both also refers to first person plural, and your is second person singular.
Mi mamá es la mayor de sus tres hermanas.
Yo soy más extrovertida/o que cualquier otro estudiante de mi aula.
