Correct Response: A. A major source of acid precipitation is the production of oxides of sulfur and nitrogen during fossil fuel combustion. These compounds combine with water in the atmosphere to form acid precipitation. Sulfur dioxide is the primary pollutant involved and power plants use flue-gas desulfurization (FGD) technologies to remove sulfur dioxide from smokestack emissions. Reacting sulfur dioxide with calcium hydroxide in a lime-water spray is a wet-scrubbing technique that can remove 95% of the sulfur dioxide in emissions. Since dust particles (B) are not the cause of acid precipitation, removing them does not diminish the problem. Carbon monoxide (C) is a pollutant produced by fossil-fuel combustion, but it is not a major cause of acid precipitation and while volatile hydrocarbons (D) are produced during fossil-fuel combustion, they are not a primary cause of acid precipitation and their removal prior to combustion is not feasible.
