This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
In a coho study nonsmokers were found to have carcinoma lung. This indicates- 
Select and explain. 
A. Smoking does not cause lung cancer, B. Etiology for lung Ca is multi factorial, C. Smoking is the only cause of lung cancer, D. Passive smoking also increase lung cancer
B: Etiology for lung Ca is multi factorial
Answer: B: Etiology for lung Ca is multi factorial 
Explanation: Coho study is also known as incidence study. The cohos are identified prior to the appearance of disease under investigation. The study group so defined are observed over a period of time to determine the frequency of disease among them. Ref: 25th edition, Park's Textbook of Preventive and Social Medicine, Page no. 83