According to the [[National Academy of Sciences]], "Of all the fossil-fuel sources, coal is the least expensive for its energy content..."[http://needtoknow.nas.edu/energy/energy-sources/fossil-fuels/coal/][[User:Conservative|Conservative]] ([[User talk:Conservative|talk]]) 01:38, 5 July 2017 (EDT) | According to the [[National Academy of Sciences]], "Of all the fossil-fuel sources, coal is the least expensive for its energy content..."[http://needtoknow.nas.edu/energy/energy-sources/fossil-fuels/coal/][[User:Conservative|Conservative]] ([[User talk:Conservative|talk]]) 01:38, 5 July 2017 (EDT) |