This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: DNB 2018, Subject name: Social & Preventive Medicine
[{'content': 'Most impoant indicator of Air pollution is:- \nSelect and explain. \nA. SO2, B. CO2, C. CO, D. N2O', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The best indicators of air pollution are sulfur dioxide, smoke and suspended paicles. Various indicators used: Chemical: SO2 , NO2, CO, Air pollution index, Soiling index, Coefficient of haze. Biological: Lichens BEST Overall- SO2', 'role': 'assistant'}]