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': 'In a population of 5000, incidence of disease is 100 in 1 year. Duration of disease studied for is 2 years. Calculate prevalence \nSelect and explain. \nA. 20\\/1000, B. 40\\/1000, C. 80\\/1000, D. 400\\/1000', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ref: Parks 23rd edition pg 61. Prevalence = Incidence x Duration = (100/5000) x 2 = (20/1000) x 2 = 40/1000', 'role': 'assistant'}]