It Is the Custom for Paper Mills Located Alongside the Layzee

It is the custom for paper mills located alongside the Layzee River to discharge waste products into the river. As a result, operators of hydroelectric power-generating plants downstream along the river find that they must clean up the river's water before it flows through their equipment.In the situation described above, we would expect an

A) overproduction of paper in the mills.
B) underproduction of paper in the mills.
C) external cost resulting from the production of hydroelectric power.
D) overproduction of power by the hydroelectric plants.