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
All are indicators for air pollution, except - 
Select and explain. 
A. CO, B. SO2, C. Soiling Index, D. Smoke index
A: CO
Answer: A: CO 
Explanation: Indicators of air pollution: Smoke (soiling) index Sulphur dioxide Grit and dust measurement Coefficient of Haze Air pollution index CO is not an index! Park's Textbook of Preventive and Social Medicine, 25th edition, Page No.796