<prompt> In a coho study nonsmokers were found to have carcinoma lung. This indicates-Smoking does not cause lung cancerEtiology for lung Ca is multi factorialSmoking is the only cause of lung cancerPassive smoking also increase lung cancer  <response>: 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, Parks Textbook of Preventive and Social Medicine, Page no. 83 