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: ENT
[{'content': 'Nasopharyngeal carcinoma causes deafness by -a) Blocking the Eustachian tubeb) Serous otitis mediac) Temporal bone metastasisd) Radiation \nSelect and explain. \nA. ab, B. a, C. ad, D. bc', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Nasopharyngeal carcinoma can cause obstruction of eustachian tube which results in serous otitis media and conductive deafness.', 'role': 'assistant'}]