The ball will continue to move at a constant speed until another force acts on it or it hits an obstacle.
The motion of the ball when the student stops pushing it depends on the forces acting on the ball. In this case, the ball is pushed on a flat, frictionless surface, which means there is no force to slow it down. Therefore, the ball will continue to move at a constant speed (option a) until another force acts on it or it hits an obstacle.