In Arumville, among those young children with elevated levels of lead in their blood, few live in houses containing lead-based paint, but many live in areas where vehicular traffic is heavy. These children' s elevated blood-lead levels probably result from lead added to gasoline, since, although gasoline sold in and around Arumville has been lead-free since 1990, lead from vehicle exhaust remains in the soil for many years. Which of the following, if true, most strengthens the argument? ["In Arumville, children's blood-lead levels typically rise during the warm summer months when children frequently play outdoors but not in the winter when children spend more time indoors.", 'Sales of lead-based paint for use in homes was banned in Arumville in 1977.', 'Vehicle traffic in most residential areas of Arumville is heavier today than it was twenty years ago.', 'If improperly carried out, the removal of lead-based paint from older houses can significantly increase the risk that children living in such houses will ingest lead dust.']