For a roller coaster as shown in the figure, which one of the following is correct? A Potential energy at the mean position (point 3) is one-half of the potentials at points 2 and 4. B Kinetic energies at the two extreme positions (points 1 and 5) are equal but non-zero. C Kinetic energies at the two extreme positions (points 1 and 5) are equal and zero. D Potential energy at the mean position (point 3) is twice of the potential at point 2 or at point 4.