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 a disease depends upon the following- \nSelect and explain. \nA. Incidence, B. Duration, C. Both of the above, D. None of the above', 'role': 'user'}, {'content': 'Answer: C \nExplanation: .prevalence of a disease can be calculated as prevalence is the product of incidence and the mean duration of the illness. ref:parks textbook ,22nd edition,pg no 59', 'role': 'assistant'}]