Four systems are described below. For which system is the subsequent motion most consistent with simple harmonic motion?
a) A simple pendulum released from an initial angle of 45∘ with no air resistance
b) A block attached to a spring on a horizontal surface that experiences a constant kinetic friction force
c) A block attached to an ideal spring oscillating on a frictionless horizontal surface after being displaced a small distance
d) A frictionless cart that oscillates back and forth just over the crest of a parabolic hill