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 in audiogram is deepest at the frequency of: \nSelect and explain. \nA. 0.5 kHz, B. 2 kHz, C. 4 kHz, D. 8 kHz", 'role': 'user'}, {'content': "Answer: B \nExplanation: (b) 2kHz or 2000Hz(Ref. Scott Brown, 8th ed., Vol 2 1070)In otosclerosis there is an increase in BC threshold of approx. 5dB, 10dB and 15dB at 500,1000,2000Hz respectively. So the deepest dip is at 2kHz which is known as Carhart's notch.At 4or8kHz, there is no hearing loss in otosclerosis.", 'role': 'assistant'}]