The correct answer is B to C.
From the law of conservation of energy, energy can neither be created nor be destroyed but can be converted from one form to another.
Potential energy is the form of energy that is possessed by an object due to its height. The kinetic energy is the form of energy that is possessed by an object due to its motion.
The gravitational potential energy of the roller coaster will be maximum when it is at the maximum height and it will decrease with the decreasing height.
Its kinetic energy will be maximum when it has a maximum velocity.
Thus the roller coaster will have maximum kinetic energy at point B. And as it rises on the track towards point C, it will lose its kinetic energy which will be transformed into potential energy.
Thus as the roller coaster moves from B to C, its kinetic energy will be transformed