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: Radiology
[{'content': 'Half life of Rn-222 is: \nSelect and explain. \nA. 3 days, B. 3-6 days, C. 4 days, D. 5 days', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. 3-6 days', 'role': 'assistant'}]