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': 'Cobalt 60 is: \nSelect and explain. \nA. Naturally occurring radioisotope, B. Aificial radioisotope, C. Product of plutonium, D. Product of uranium', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. Aificial radioisotope', 'role': 'assistant'}]