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': 'A pandemic of H1N1 is suspected when? \nSelect and explain. \nA. Cases occur within 2 weeks period, B. Cases are spread over 5 or more cities, C. At least one or more laboratory confirmed H1N1 case, D. 25 or more people are affected', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. b. Cases are spread over 5 or more cities', 'role': 'assistant'}]