Final answer:
A motorcycle's weight remains constant as it travels over the crest of a hill because weight is the force due to gravity on an object's mass, and neither the mass nor the gravitational pull changes in this scenario.
Step-by-step explanation:
When a motorcycle travels over the crest of a hill, the weight of the motorcycle remains the same. Weight is defined as the force exerted by the gravitational pull of the Earth, which is the mass of the object multiplied by the acceleration due to gravity. This force will remain constant for an object unless the mass or gravitational pull changes, none of which happens simply by traveling over a hill. Therefore, the correct answer is C) It remains the same.