This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Otosclerosis, Subject name: ENT
[{'content': "Carhart's notch dips at: \nSelect and explain. \nA. 2 Hz, B. 200 Hz, C. 2000 Hz, D. 2000 MHz", 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. (c) 2000 Hz* Carhart Notch is an audiogram finding and is an important feature in patients with Otosclerosis.* There is a sudden dip (notch) at 2000 Hz in bone conduction curve.* Carhart s notch disappears after stapedectomy.', 'role': 'assistant'}]