The more you stretch a rubber band, the more you can feel it pulling back on your fingers. Which of Newton's laws BEST explains WHY? A. first B. second C. third

Answer: This is an example best explained by Newton's Third Law. This law is based on the observation that all forces in nature and within an isolated system occur in symmetry, that is, for every force exerted on an object there is a force equal in magnitude and with opposite direction (counter-acting force). This has a consequence that the net force of an isolated system is always zero - in other words a system cannot set itself into motion by generating a net force acting on itself.

The rubber band pulling back is due to the force counteracting your force you exert on the rubber band. The magnitude will be proportional to that of your action.