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': 'Aificial radioisotops: \nSelect and explain. \nA. Radium, B. Uranium, C. Plutonium, D. Iridium', 'role': 'user'}, {'content': 'Answer: D \nExplanation: D i.e. Iridium', 'role': 'assistant'}]