Why Do Coal-Burning Power Plants and Oil Refineries Have Tall

Why do coal-burning power plants and oil refineries have tall smokestacks?

A) To utilize the scrubbers in the smokestacks that remove pollutants
B) To make use of the natural vertical movements of air
C) To vent exhausts high into the atmosphere for dilution and dispersal
D) To exploit the presence of mountains
E) to avoid photochemical reactions with ozone near the ground