In English grammar, a pronoun is a word that is used instead of the noun.
A basic example is "Sarah is tall". In this sentence, Sarah is a noun. Because we know that Sarah is a girl, we can use the pronoun she and keep the same meaning - "She is tall".
Easy, right? Well then, take a look at the following ten sentences and choose the correct pronoun.
Link: How to use Subject Pronouns and Object Pronouns