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: Unknown
[{'content': 'Type of sphenoid sinus in adult population is usually: \nSelect and explain. \nA. Sellar, B. Post seller, C. Pre seller, D. Maximal Pneumatization', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The types of the sphenoid sinus can be classified in three groups in the adult: I. conchal, II. presellar, and III sellar types, depending on the extent to which the sphenoid bone is pneumatized.\nIn the conchal type, the area below the sella is a solid block of bone without an air cavity.\nIn the presellar type, the sphenoid sinus has moderate air cavity with no sellar indentation.\nIn the sellar type, which is the most common, the corpus of the sphenoid is well pneumatized with full indentation of the sella into the sinus and extends posteriorly until the clivus\nThe conchal type is most common in children and infrequent in the adult (Rhoton).', 'role': 'assistant'}]