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
Sinusitis is least involved in - 
Select and explain. 
A. Maxillary, B. Ethmoid, C. Frontal, D. Sphenoid
D: Sphenoid
Answer: D: Sphenoid 
Explanation: None