C. Increased combustion causing more air pollution.
Explanation:
"Urbanization" refers to a situation wherein many people move to the city to live and leave the rural area behind. This means that the population of the city increases. The more people living in the city, the more vehicles there are. Vehicles work through<u> combustion,</u> which produces <em>pollutants into the air. </em>So this means that<u> the increasing number of vehicles results to an increasing amount of air pollution.</u>
