Answer:
Some.
Step-by-step explanation:
A quantifier is a word used before a noun to show the quantity of the object. A quantifier is also used in the place of a determiner in a sentence.
Examples of quantifiers are some, few, little, lots of, not many, many, etc.
In the given sentence, the quantifier that correctly fits the fill-up is some.
The correct sentence would be,
"Some people read a lot of books."
Therefore, some is the correct answer.