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 part of middle ear is - 
Select and explain. 
A. Hypotympanum, B. Epitympanum, C. Attic, D. Mesotympanum
D: Mesotympanum
Answer: D: Mesotympanum 
Explanation: “When seen in coronal section, the cavity of the middle ear is biconcave, as the medial and lateral walls are closest to each other in the center.”
The distances separating them are:

Near the roof 6 mm → Epitympanum (Attic)
In the centre 2 mm → Mesotympanum

           (between promontary and umbo)

Near the floor 4 mm → Hypotympanum