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".
Q: A group of people are riding on horses on a field. They start a game of polo. they <sep> (A) continue to play on the horses. (B) make a great team and win several goals. (C) hit balls into the goal and continue to ride the horses. (D) race their horses, trying to get the ball.
A:
D