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: B i.e. 5.2 years', 'role': 'assistant'}]