Concept:Oxides of nitrogen are mainly produced when fuels burn at high temperatures, causing atmospheric nitrogen and oxygen to react.Explanation:During the combustion of fuel in engines or power plants, temperatures become high enough for nitrogen in air to combine with oxygen:N2+O2→2NOThis nitrogen monoxide is further oxidized to nitrogen dioxide, contributing to air pollution.Coal and wood also produce some oxides, but the major general source is the burning of fuel.Answer:C. fuel