Correct Option: A

Carbon monoxide (CO) is considered a pollutant since it is toxic to hemoglobic animals (including humans) when encountered in concentrations above about 35 ppm. It combines with hemoglobin to produce carboxyhemoglobin, which usurps the space in hemoglobin that normally carries oxygen, but is ineffective for delivering oxygen to bodily tissues. A level of 50% carboxyhemoglobin may result in seizure, coma, and fatality.