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
Bilateral phrenic nerve palsy is caused by ? 
Select and explain. 
A. Carcinoma bronchus, B. Polio, C. Medullary carcinoma thyroid, D. Paget's disease
B: Polio
Answer: B: Polio 
Explanation: Ans. is 'b' i.e., Polio