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
[{'content': 'Which of the following statement is true - \nSelect and explain. \nA. Case control study is not suitable for rare diseases, B. Cohort study involves large number of subjects, C. Case-control study is relatively expensive, D. Cohort study yields relatively quick results', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Cohort study involves large number of subjects* Prevalence of blindness in India: 700 per 1 lakh population (0.7%) if cut of criteria is < 3/60 (WHO criteria); or 1100 per lakh population (1.1%) if cut of criteria is < 6/60 (NPCB criteria).", 'role': 'assistant'}]