<human>: I've heard that there's a big problem with pollution in the United States. What are the main causes of pollution?
<bot>: The main causes of pollution in the United States are emissions from cars and trucks, factories, power plants, and other sources. These emissions include carbon dioxide, sulfur dioxide, nitrogen oxides, and particulate matter. These pollutants can cause health problems such as asthma, lung cancer, heart disease, and respiratory illnesses.