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': 'Criteria for defining polio epidemic are all except - \nSelect and explain. \nA. 2 or more cases, B. Cases should occur in same locality, C. Caused by same virus type, D. Cases occurring during 6 month period', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]