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': 'Orbital cellulitis most commonly occurs after infection of which of the following sinuses? \nSelect and explain. \nA. Maxillary sinus, B. Frontal sinus, C. Ethmoidal sinus, D. Sphenoidal sinus', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Bacterial orbital cellulitis is most commonly caused by the spread of infection in the ethmoid sinus into the orbit directly through the lamina papyracea or by travelling through the anterior and posterior ethmoid vessels.', 'role': 'assistant'}]