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': "All are the indicators of air pollution except \nSelect and explain. \nA. Soiling index, B. McArdle's index, C. Suspended paicle count, D. SO2 concentration", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Air pollutants can be of several types : Primary pollutants: are emited directly (SO2, NO2, CO, Hydrocarbons, Paiculate matter, CFCs, Ammonia, Radioactive materials, Metals like lead , cadmium, copper, Volatile organic compound) Secondary pollutants: are formed by interaction between primary pollutants (Ground level ozone, peroxyacetyl nitrate, Paiculate matter formed from primary polluntants ) Chemicals indicators of air pollution: Sulphurdioxide: Best indicator of air pollution Smoke or soiling index: Air strain on a filter paper measured through photoelectric meter Grit and dust measurement Coefficient of haze Air pollution index BEST Biological indicator of air pollution: Lichens. Ref: Park 25th edition PGno: 770-772', 'role': 'assistant'}]