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
[{'content': 'Sinusitis is least involved in - \nSelect and explain. \nA. Maxillary, B. Ethmoid, C. Frontal, D. Sphenoid', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]