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
[{'content': 'Sinusitis which is least involved is? \nSelect and explain. \nA. Maxillary, B. Ethmoid, C. Frontal, D. Sphenoid', 'role': 'user'}, {'content': "Answer: D \nExplanation: Sinusitis is least involved in the sphenoid sinus. Isolated involvement of this sinus is rare. It's often pa of pansinusitis or is associated with infection of posterior ethmoid sinuses. (Reference: Textbook of PL Dhingra and Shruti Dhingra; 7th edition, pg no. 216)", 'role': 'assistant'}]