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
Narrowest pa of middle ear is: 
Select and explain. 
A. Hypotympanum, B. Epitympanum, C. Attic, D. Mesotympanum
D: Mesotympanum
Answer: D: Mesotympanum 
Explanation: 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.