Answer:
C
Explanation:
I think it could be C because obviously a good sentence needs a Good noun, and article, verb, adjective.
Las cosas que hice el el mes pasado es que you fui a la playa con mis amigos y luego fuimos a downtown a caminar y divertirnos.
The answer is usan because it is talking about how they talk to their friends. They USE slang.
