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': 'Mucocele is commonly seen in sinus: \nSelect and explain. \nA. Frontal, B. Maxillary, C. Ethmoid, D. Sphenoid', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A mucocele is an epithelial lined, mucus containing sac completely filling the sinus and capable of expansion: Mucocele are most commonly formed in Frontal sinus followed by ethmoid, sphenoid and maxillary sinuses. Mucocele of frontal sinus presents as a swelling in the floor of frontal sinus above the inner (medial) canthus. It displaces the eyeball forward, downward and laterally. IOC = CT scan TOC Endoscopic sinus surgery', 'role': 'assistant'}]