Near many cities, contamination of lakes and rivers from pollutants in rainwater runoff exceeds that from industrial discharge. As the runoff washes over buildings and pavements, it picks up oil and other pollutants. Thus, water itself is among the biggest water polluters. The statement that contamination of lakes and rivers from pollutants in rainwater runoff exceeds that from industrial discharge plays which one of the following roles in the argument? ['It is a conclusion for which the claim that water itself should be considered a polluter is offered as support.', 'It is stated to provide an example of a typical kind of city pollution.', 'It is a premise offered in support of the conclusion that water itself is among the biggest water polluters.', 'It is a generalization based on the observation that rainwater runoff picks up oil and other pollutants as it washes over buildings and pavements.']