This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nose and paranasal sinuses, Subject name: ENT
Most common sinus involved in acute sinusitis? 
Select and explain. 
A. Ethmoid, B. Maxillary, C. Sphenoid, D. Frontal
B: Maxillary
Answer: B: Maxillary 
Explanation: The sinus most commonly involved is the maxillary followed in turn by ethmoid, frontal and sphenoid. (Ref: Diseases of ENT, PL Dhingra, 7th edition, of no. 213)