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: Anatomy
[{'content': 'First sinus developed: \nSelect and explain. \nA. Maxillary sinus, B. Frontal sinus, C. Sphenoidal sinus, D. Ethmoidal sinus', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]