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
Most impoant indicator of Air pollution is:- 
Select and explain. 
A. SO2, B. CO2, C. CO, D. N2O
A: SO2
Answer: A: SO2 
Explanation: 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