This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Physics of Radiotherapy, Subject name: Radiology
[{'content': 'Half life of I 131 is: (Repeat) \nSelect and explain. \nA. 13 days, B. 8 days, C. 2 days, D. 12 hours', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans: B (8 days) Ref: Internet SourceExplanation:Refer JIPMER 2012 Radiology.', 'role': 'assistant'}]