Our mother said, "You should visit your grandparents as much as you can because you will never know when she will be gone from your life". Author's purpose:

The authors purpose is to tell people that you don't know someone is going to pass away so you need to spend time time with them

the answer is

i say that the right answer is: three personal subject pronouns. that’s because you will see “she” two times, referring to the librarian, and “they” one time, referring to the books. personal subject pronouns are used to replace common nouns or proper names.

the only possessive noun it’s present on the first sentence, when the speaker refers to “his” father.