This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ear, Subject name: ENT
[{'content': 'The distance between tympanic membrane and medial wall of middle ear at the level of centre is: \nSelect and explain. \nA. 3 mm, B. 4 mm, C. 6 mm, D. 2 mm', 'role': 'user'}, {'content': 'Answer: D \nExplanation: (d) 2mm(Ref. BD Chaurasia, Human Anatomy 6th ed., Vol 3, page 277)Part of the middle ear cavityDistance from lateral to medial wallEpitympanum6mm (widest)Mesotympanum (centre)2mm (narrowest)Hypotympanum4mm', 'role': 'assistant'}]