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 of the following are indicators of air pollution except 
Select and explain. 
A. CO, B. SO2, C. Soiling index, D. Smoking index
D: Smoking index
Answer: D: Smoking index 
Explanation: Soiling index or smoke index is used to monitor air pollution. Best indicators of air pollution are sulfur dioxide, smoke index, grit and dust measurement, coefficient of haze and Air pollution index. Smoking index is measured by multiplying the number of cigarettes smoked per day by the number of years the person has smoked. Park's Textbook of Preventive and Social Medicine, 25th Edition, Pg 796