sentences: many vehicles emit pollution into the air
docs: motor_vehicle is mobile_artificial_pollution_source. automobile_exhaust is pollutant. air_pollution is pollution. air_pollution is polluting. cars is major_cause_of_pollution. combustion_of_fossil_fuels is common_source_of_air_pollution. automobile_emissions is major_component_of_smog. city_of_los_angeles has air_pollution car has filter