Answer:
The correct answer is: they study.
Step-by-step explanation:
TRANSLATION:
In the bookstore, friends study.
The correct answer is a. they study. The why:
It would be correct to say: "study" because they are in a library. While they could dance or eat inside the library, the prayer would not be congruent as if it were said "study in the library."
I hope it has served you, good luck!