Solutions
‘Few’ The adjective requires here is for the countable noun, i.e. books. "A little" would be an incorrect choice here as it is used for uncountable nouns. Now, the fight is between "few" and "a few". "The few" would be incorrect to use here.
The difference between "few" and "a few" is explained below:
"few" = not very many, with a focus on the fact that this number is (remarkably) small.
"a few" = not very many, but at least more than one
Let's understand it with some examples:
"I have a few friends" is just the same as saying "I have some friends".
"I have few friends", however, implies that you don't have many friends (as opposed to many). In some contexts (not always!), it can also imply that you don't feel very well about it, that you wish you had more friends.
Here, the sentence mentions that there are barely any books in the library, so the correct filler here would be "few".