Most people don’t try hard enough to see the other fellow’s problem.

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.