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': 'Maxillary sinus achieves maximum size at: \nSelect and explain. \nA. At bih, B. At primary dentition, C. At secondary dentition, D. At pubey', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Maxillary sinus is the first sinus to develop at bih.It is completely developed by 9 years of age, i.e. approximately at the time of secondary dentition.', 'role': 'assistant'}]