This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
[{'content': 'Soiling index determines: March 2012 \nSelect and explain. \nA. Contraception failure, B. Air pollution, C. Number of hookworm eggs, D. Ratio of mucus secreting glands to thickness of wall of airways', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans: B i.e. Air pollution Indices and their significance Pearl index, used for measuring contraceptive efficacy, is defined as the number of \'failures per 100 woman-years of exposure (HWY)," Smoke/ soiling index is used for monitoring air pollution Chandler worked out an index on the basis of average number of hookworm eggs per gram of faeces for the entire community, known as Chandlers index Reids index is defined as ratio between the thickness of the submucosal mucus secreting glands and the thickness between the epithelium and cailage that covers the bronchi.', 'role': 'assistant'}]