This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
[{'content': 'The best parameter to measure air pollution is: \nSelect and explain. \nA. SO2, B. CO2, C. CO, D. N10', 'role': 'user'}, {'content': 'Answer: A \nExplanation: SO2', 'role': 'assistant'}]