Although large cities are generally more polluted than the countryside, increasing urbanization may actually reduce the total amount of pollution generated nationwide. Residents of large cities usually rely more on mass transportation and live in smaller, more energy-efficient dwellings than do people in rural areas. Thus, a given number of people will produce less pollution if concentrated in a large city than if dispersed among many small towns.

Which one of the following most accurately describes the role played in the argument by the claim that increasing urbanization may actually reduce the total amount of pollution generated nationwide?