You indicated that the acceleration at point D is zero. An object with zero acceleration is either sitting at rest for a period of time or is moving with constant speed in a straight line. Is either of these true at point D?

 

In addition, remember that at point D the ball is flying through a vacuum. Hence, the acceleration of the ball at point D is the freefall acceleration (i.e., the acceleration of gravity). In what direction is the freefall acceleration?