The correct description of the energy transformation as the model roller coaster rolls from point X to point Y is:
Potential energy transfers to kinetic energy, then some kinetic energy transfers to potential energy.
At point X, the roller coaster has maximum potential energy due to its height. As it moves downward toward point Y, this potential energy is converted to kinetic energy, causing the roller coaster to accelerate. When it reaches a lower point and begins to ascend again, some of that kinetic energy is converted back into potential energy.