The flux linked with the copper tube will change because of the motion of the magnet. This will produce an eddy current in the body of the copper tube. According to the Lenz's law, the direction of the induced current is such that it opposes the magnetic field that has induced it. So the induced Current will be in the opposite direction to the magnet field of the bar magnet. And it will slow the fall of the magnet. Then negative acceleration nothing retarding force will act on the bar magnet. If the velocity of the magnet is increased then the retarding force will also increase. And it will happen up to this retarding force is equal to the force of gravity. Then the total force acting on the bar magnet will become zero. Then the magnet will move with almost a constant speed. So option B is correct.