In which of the following sentences is the underlined word an object pronoun?
a. you really should apologize to her.
b. we returned our books to the library.
c. i would like you to listen to me.
d. i gave her a gift for her birthday.

A pronoun is a word that takes the place of a noun. For example :
I, me, he, she, herself, you, it, that, they, each, few, many, who, whoever, whose, someone, everybody, etc.
In the sentences above the right answer lies in the option : 
B. We returned our books to the library. 
OUR is the pronoun.

your a very good friend :)

Explanation: