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': 'Acoustic dip occurs at - \nSelect and explain. \nA. 2000Hz, B. 4000 Hz, C. 500Hz, D. 1500 Hz', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Acoustic dip is dip seen in pure tone audiometry due to noise trauma, which is seen typically at 4 kHz i.e. 4000 Hz.', 'role': 'assistant'}]