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': 'Which is not a pa of paranasal sinus? \nSelect and explain. \nA. frontal, B. Ethmoid, C. Sphenoid, D. Pyriform', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Paranasal sinuses are air containing cavities in ceain bones of skull. They are four on each side. Clinically,paranasal sinuses have bern divided into Anterior-Maxillary,Frontal, Anterior ethmoidal. posterir-Posterior ethmoid,sphenoid sinus. Ref Dhingra 6/e,p 187.', 'role': 'assistant'}]