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
True about sphenoid sinus - 
Select and explain. 
A. Lined by stratified squamous epithelium, B. Duct open in middle meatus, C. Open in sphenoethmoid recess, D. Present at birth
C: Open in sphenoethmoid recess
Answer: C: Open in sphenoethmoid recess 
Explanation: All paranasal sinuses are lined by respiratory epithelium (i.e. ciliated pseudo stratified columnar epithilium) i.e. option a is incorrect.

Sphenoid sinus: Important points

It is not present at birth
It occupies the body of sphenoid
Ostrum of sphenoid sinus is situated in the upper part of anterior wall and drains into spheno ethmoidal recess.
On x ray: Sphenoid sinus is visible by 4 years of age.