Definition: 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".
Input: A group of dirt bikers are prepared at the gate. the gate <sep> (A) opens and the dirt bikes begin to race with each other in an energetic race. (B) is pulled down, and a ramp is attached. (C) is opened and they start a race on bikes. (D) opens, and they take off.
Output:
D