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': "The' 1/2 life of 1131 is: \nSelect and explain. \nA. 8 hours, B. 2 days, C. 5.2 days, D. 8 days", 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. 8 days', 'role': 'assistant'}]