This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diagnostic and operative ENT, Subject name: ENT
[{'content': 'Caldwell luc approach opens \nSelect and explain. \nA. Maxillary sinus, B. Frontal sinus, C. Sphenoid sinus, D. Ethmoid sinus', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Caldwell luc approach opens maxillary sinus. Ref- Dhingra, 6th edition, Page 412.', 'role': 'assistant'}]