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: Anatomy
[{'content': 'Cavernous sinus thrombosis happens when infection reaches at \nSelect and explain. \nA. Ethmoidal vein., B. Maxillary sinus, C. Pterygoid plexus of vein., D. Submental lymph nodes.', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]