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': 'Type Ad curve is seen in - \nSelect and explain. \nA. Eustachian tube obstruction, B. After stapedectomy, C. Middle ear tumours, D. Secretory otitis media', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., After stapedectomy", 'role': 'assistant'}]