Q: In this task, you are given a context and four options. Each option is a suggested ending for the context. You should read the context and pick the best ending for the context. Please answer with "A", "B", "C", and "D". 
A girl in a bathing suit is sitting on the beach. she <sep> (A) is laying down on the ground picking up sand. (B) begins doing sit ups on the beach. (C) is holding the camera while treading water. (D) is putting sand into a cup and building a sand castle.
A:
D