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: Medicine
[{'content': 'MacCullum plaques in acute rheumatic fever are usually seen in \nSelect and explain. \nA. Right atrium, B. Left atrium, C. Right ventricle, D. Left ventricle', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]