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': 'Narrowest pa of middle ear is: \nSelect and explain. \nA. Hypotympanum, B. Epitympanum, C. Attic, D. Mesotympanum', 'role': 'user'}, {'content': 'Answer: D \nExplanation: When seen in corona section, the cavity of the middle ear is biconcave, as the medial and lateral walls are closest to each other in the center.', 'role': 'assistant'}]