Which of the following pollutants is main product of automobile exhaust ?

Cars burn fuel to run. When fuel burns completely, it mainly produces carbon dioxide (CO2).
However, when the burning isn't perfect (like when a car isn't well-maintained), other things are also produced.
One very important one is carbon monoxide (CO). This is a poisonous gas.
Other things found in car exhaust include nitrogen oxides (NO) and unburnt hydrocarbons.
But, of the choices given, carbon monoxide (CO) is a major component of automobile exhaust, often present in higher amounts than the others due to incomplete combustion.
Therefore, the correct answer is A: CO.