This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Head and neck, Subject name: Anatomy
[{'content': 'All open into middle meatus except \nSelect and explain. \nA. Frontal sinus, B. Sphenoid sinus, C. Maxillary sinus, D. Ethmoidal sinus', 'role': 'user'}, {'content': 'Answer: B \nExplanation: THE FOLLOWING FEATURES ARE: 1.Ethmoidal bulla 2.Hiatus semilunaris 3.Infundibulum 4.Opening of frontal air sinus 5.Opening of anterior ethmoidal sinus 6.Opening of maxillary sinus Ref BDC volume 3,sixth edition pg 243', 'role': 'assistant'}]