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
If incidence = 50 cases/1000 population/year and mean duration of disease = 5 years, then prevalence would be: 
Select and explain. 
A. 10, B. 250, C. 10-Jan, D. 1/250
B: 250
Answer: B: 250 
Explanation: None