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': 'The distance between tympanic membrane and medial wall of middle ear at the level of center is - \nSelect and explain. \nA. 3mm, B. 4 mm, C. 6mm, D. 2 mm', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]