Question

Christian monks taught laypeople the art of stained glass, which served which of the following functions in medieval Europe?

Answer 1

It taught religious scripture to illiterate peasants through images!

(It's B.)

Answer 2

Christian monks taught laypeople the art of stained glass, which served to teach religious scripture to illiterate peasants through images.
Since these peasants didn't know how to read, they had to be taught about religion in one way or another. So, paintings were used for such a purpose.