Please Help! (I showed the paragraph with the question.)

According to the author, what effect do the cart’s wheels have on most roller coasters?

When the cart reaches the top of the first hill, not only are riders’ stomachs screaming for mercy, but also the cart is at its maximum potential energy. Without warning, the energy-loaded cart begins to descend the first hill. As the cart careens down the hill, it has kinetic energy. Kinetic energy is different from potential energy. Kinetic energy is the energy of motion. All objects in motion have this energy. The kinetic energy propels that cart down the hill. Eventually, the cart will fight the forces of gravity and travel up another hill. On this uphill journey, the cart again begins to gain potential energy. The cart switched from potential energy, to kinetic energy, and back again. Therefore, a roller coaster ride is just the converting of kinetic energy and potential energy.

a) The wheels cause friction
b) The wheels eliminate friction
c) order of importance
d) comparison and contrast