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': 'Atrial fibrillation may occur in all of the following conditions, except - \nSelect and explain. \nA. Mitral stenosis, B. Hypothyroidism, C. Dilated cardiomyopathy, D. Mitral regurgitation', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]