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': "In otosclerosis Carhart's notch dips at: \nSelect and explain. \nA. 1000 Hz in AC, B. 1000 Hz in BC, C. 2000 Hz in AC, D. 2000 Hz in BC", 'role': 'user'}, {'content': "Answer: D \nExplanation: (d) 2000HzinBC(Ref. Shambaugh, 6th ed., 532)In otosclerosis the dip at 2000Hz is seen in bone conduction curve which is known as Carhart's notch. Mnemonic: Carhart's in Bone Conduction, CBC.", 'role': 'assistant'}]