Rivers usually empty into oceans. Any pollution deposited or pick-up by the river, will eventually end up in the ocean.
Its only 5 points, not 88
A closed system is a system that makes no physical or chemical exchanges with its environment. Of these systems provided as choices (tree, human, clock, car), only a clock does not make exchanges with the environment, except for energy.
Therefore, of that list, only a clock would be a closed system.
Hope that helped! =)
