Question:
What is the antecedent of the pronoun those?
Sentence: Those are books that need to be returned to the library
Answer:
Books
Pronouns are used to replace nouns with more general terms that don't describe a specific person or place. The antecedent of a pronoun is the word that the pronoun replaces.
In the case of this sentence, the pronoun those replaces the word books, therefore the antecedent of the pronoun those is books.