This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Congenital Lesions and Stridor, Subject name: ENT
[{'content': 'Sinus not present at birth is: \nSelect and explain. \nA. Ethmoid, B. Maxillary, C. Frontal, D. None', 'role': 'user'}, {'content': 'Answer: C \nExplanation: (c) Frontal(Ref. Cummings, 6th ed., 2874; Scott Brown, 8th ed., Vol 2, page 262)This is the last sinus to develop. It is not present at birth.', 'role': 'assistant'}]