This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, Subject name: Social & Preventive Medicine
[{'content': 'Among the following, which of the following is/are the greatest contributors to global warming as a consequence of human activities and life style ? \nSelect and explain. \nA. Carbon dioxide, B. Chlorofluorocarbons, C. Methane, D. Ozone', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Carbon dioxide is not commonly regarded as an air pollutant it is a natural constituent of air. It does not take pa in any significant chemical reactions with other substances in the air However, it could increase global temperature enough to affect climate markedly', 'role': 'assistant'}]