The answer below.
Work Step by Step
It depends on the acceleration of the bus, for while you will appear to be throwing the ball straight up, it will have an x velocity equal to that of the bus. Thus, if the bus has a negative acceleration, the ball will land in front of the bus, but if the bus has a positive acceleration, the ball will land behind the bus. Finally, if the bus has a constant velocity, the ball will return to your hand.