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': 'Prevalence of cataract at one point of time can be determined by - \nSelect and explain. \nA. Longitudinal study, B. Cross sectional study, C. Surveillance, D. Coho study', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Cross-sectional study provides information about disease prevalence but it provides very little information about the natural history of disease or rate of occurrence of new cases (refer park pgno:69 23 rd edition)', 'role': 'assistant'}]