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: Surgery
[{'content': "Bilateral phrenic nerve palsy is caused by - \nSelect and explain. \nA. Carcinoma bronchus, B. Polio, C. Medullary carcinoma thyroid, D. Paget's disease", 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]