This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Eye, Nose and Ear, Subject name: Anatomy
[{'content': '59-year-old man has difficulty in breathing through his nose. On examination, his physician finds that he has swelling of mucous membranes of the superior nasal meatus. Which opening of the paranasal sinuses is most likely plugged? \nSelect and explain. \nA. Middle ethmoidal sinus, B. Maxillary sinus, C. Anterior ethmoidal sinus, D. Posterior ethmoidal sinus', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Posterior ethmoidal sinus opens into the superior nasal meatus. Maxillary, frontal, and anterior and middle ethmoidal sinuses drain into middle nasal meatus.', 'role': 'assistant'}]