runoff from a cropland causes water pollution
water_pollution is pollution. cars is not major_cause_of_pollution. crop_farm is cropland. cars is major_cause_of_pollution. acid_rain is not form_of_pollution. acid_rain is not serious_form_of_pollution. acid_rain is serious_form_of_pollution. acid_rain is form_of_pollution. runoff is surplus. littering is polluting.