The correct option is D causes less air pollution
Natural gas tops other fossil fuels when it comes to clean burning. Since the process of natural gas combustion is almost up to the mark, the level of byproducts disseminated to the environment is little. In addition, advances in technologies have massively reduced nitrogen oxide, a common pollutant emitted by natural gas. The blue flame witnessed during the process of burning natural gas is an indication that the gas is burning perfectly.