This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nose and PNS, Subject name: ENT
[{'content': 'Sinusitis is LEAST involved in \nSelect and explain. \nA. Maxillary, B. Ethmoid, C. Frontal, D. Sphenoid', 'role': 'user'}, {'content': 'Answer: D \nExplanation: (Sphenoid) (181- Dhingra 4th)* Most common sinus involved is - Maxillary* Least common sinus involved in - Sphenoid* Order of sequence - Maxillary >ethmoid > frontal > sphenoid', 'role': 'assistant'}]