You indicated that the acceleration at point D is perpendicular to the velocity. If the angle between the ball's velocity and acceleration is 90°, then the ball is turning but is neither speeding up nor slowing down. Is this true?

 

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?