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': 'Which of the following is not an aificial radio isotope element? \nSelect and explain. \nA. CO 60, B. 1-125, C. Ra226, D. CO59', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. CO59', 'role': 'assistant'}]