This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
[{'content': 'If incidence = 50 cases/1000 population/year and mean duration of disease = 5 years, then prevalence would be: \nSelect and explain. \nA. 10, B. 250, C. 10-Jan, D. 1/250', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]