If Burning Low-Sulfur Coal Significantly Reduces the Emission of Sulfurous

If burning low-sulfur coal significantly reduces the emission of sulfurous fumes and therefore reduces acid rain, why don't plants in the Midwest and Great Lakes region burn only low-sulfur coal?

A) Because low-sulfur coal is expensive
B) Because unions insist that high-sulfur coal be burned
C) Because low-sulfur coal produces less energy than high-sulfur coal
D) Because most low-sulfur coal comes from the eastern United States
E) Because low-sulfur coal is inexpensive