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: Pathology
[{'content': 'Most common paranasal sinus affected by Osteoma: \nSelect and explain. \nA. Frontal sinus, B. Ethmoid sinus, C. Maxillary sinus, D. Sphenoidal sinus', 'role': 'user'}, {'content': 'Answer: A \nExplanation: sequence of involvement:\nFrontal>ethmoid>Maxillary>sphenoid.', 'role': 'assistant'}]