Two football players run into each other at midfield. We can (or cannot) realistically apply conservation of momentum to calculate the players' velocities just after the impact because A. The system of interest floats in space. B. The players are functionally isolated. C. We can treat the interaction as a collision. D. Conservation of momentum does not apply here. I said D because we do not know the masses of the players. Does that sound reasonable/logical/rational?