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': 'The prevalence of dental caries in a community in the year 2000 and 2003 was 18% and 38% respectively. The incidence of caries for the same population in three years would be: \nSelect and explain. \nA. 38%, B. 20%, C. 10%, D. 56%', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Hint:\nIncidence\xa0 = No. of new cases in a specified time (38-18 = 20%)\nPrevalence = Incidence x Duration.\xa0\xa0\nIncidence = Prevalence / Duration = P/D.', 'role': 'assistant'}]