You indicated that the direction of the acceleration at point D is the same as the direction of the velocity. When the angle between the velocity and acceleration is 0°, then the ball speeds up while moving in a straight line. Is the ball speeding up and moving in a straight line 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?