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 half life of Cobalt–60 is – \nSelect and explain. \nA. 3.4 years, B. 5.2 years, C. 1.2 years, D. 2.3 years.', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Half life of cobalt - 60 is 5.2 years.', 'role': 'assistant'}]