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': 'Contrast used for MRI – \nSelect and explain. \nA. Iodine, B. Gadolinium, C. Metvazamide, D. Pmnipaque', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Gadolinium is the most commonly used MR contrast agent.', 'role': 'assistant'}]