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': 'All open into hiatus semilunaris except \nSelect and explain. \nA. Posterior ethmoid sinus, B. Anterior ethmoid sinus, C. Frontal sinus, D. Maxillary sinus', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Hiatus semilunaris. The hiatus semilunaris is a semicircular shaped openinglocated on the lateral wall of the nasal cavity. It is a component of the ostiomeatal complex and serves as the opening for the frontal and maxillary sinuses and the anterior ethmoid air cells.', 'role': 'assistant'}]