Question

what is the primary reason for air pollution caused by vehicles?
emission of nitrogen oxides
release of carbon dioxide
production of sulfur dioxide
discharge of carbon monoxide

Explanation:

Vehicles burn fossil - fuels. During incomplete combustion of fossil - fuels in vehicle engines, carbon monoxide is produced in significant amounts. While nitrogen oxides, carbon dioxide, and sulfur dioxide are also emitted, carbon monoxide is a major pollutant due to incomplete fuel combustion in engines.

Answer:

Discharge of carbon monoxide