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? ['It is a statement offered to call into question the claim that large cities are generally more polluted than the countryside.', 'It is a claim that the rest of the argument is designed to establish.', 'It is a statement serving merely to introduce the topic to be addressed in the argument and plays no logical role.', 'It is used to support the conclusion that people should live in large cities.']