A horse is pulling a wagon up a hill at an increasing speed. Ignoring all masses except those of the horse and the wagon, which is the case:
a) the horse pulls on the wagon harder than the wagon pulls on the horse.
b) the horse pulls on the wagon less than the wagon pulls on the horse.
c) the horse pulls on the wagon just as hard as the wagon pulls on the horse?

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C. Every action has an equal and opposite reaction.