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': 'Disease rate is - \nSelect and explain. \nA. Risk of susceptibility, B. Usually expressed a percentage, C. Time period in a calendar year, D. Disease occurrence in a specified time period', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Disease rate is a measure of incidence or occurrence of disease in a population.\nIn other words, it is synonymous for incidence rate.', 'role': 'assistant'}]