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 Technetium 99 is: \nSelect and explain. \nA. 2 hours, B. 6 hours, C. 12 hours, D. 24 hours', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. 6 hours', 'role': 'assistant'}]