This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Social & Preventive Medicine
[{'content': 'The best indicator for determining the general level of air pollution in an urban area is \nSelect and explain. \nA. Sulphur dioxide, B. Carbon dioxide, C. Hydrogen, D. Nitrogen', 'role': 'user'}, {'content': 'Answer: A \nExplanation: (A) Sulphur dioxide > Best indicators of air pollution are sulphur dioxide, smoke, suspended particles.# Monitoring of air pollution> Best indicators of air pollution are sulphur dioxide, smoke and suspended particles> These are monitored on a daily basis over several sites. The results are then collected by a central agency.> Sulphur dioxide: This gas is a major contaminant in many urban and industrial areas. Its concentration is estimated in all air pollution surveys,', 'role': 'assistant'}]