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: Social & Preventive Medicine
[{'content': 'Period Prevalence is \nSelect and explain. \nA. No of cases in a given point of time, B. No of cases in a given year, C. No of cases over a period of years mentioned, D. Incidence of no of cases during a given period', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]