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': 'Isotope used in RAIU – \nSelect and explain. \nA. I131, B. I123, C. I125, D. I127', 'role': 'user'}, {'content': 'Answer: B \nExplanation: RAIU stands for radioactive iodine uptake. It is a thyroid imaging method that measures the fraction of orally administered iodine isotope taken up by thyroid. 1123 is the agent of choice for RAIU.', 'role': 'assistant'}]