Question

an increased demand for books during the 1500s meant that
fewer books were written in the vernacular.
more books were written in the vernacular.
fewer people read classical works
more people read chinese works.

Explanation:

During the 1500s, with an increased demand for books, authors and publishers would want to reach a wider audience. Writing in the vernacular (the common language of the people) would allow more people to read the books. So, an increased demand for books would lead to more books being written in the vernacular. There is no indication in the general context of the 1500s related to the demand - book relationship that fewer books in vernacular would be the case. Also, there is no connection shown between increased book demand and fewer people reading classical works or more people reading Chinese works in this general statement about book demand.

Answer:

more books were written in the vernacular.