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: Ophthalmology
[{'content': 'Paralysis of 3rd, 4th, 6th nerves with involvement of ophthalmic division of 5th nerve, localizes the lesion to - \nSelect and explain. \nA. Cavernous sinus, B. Apex of orbit, C. Brainstem, D. Base of skull', 'role': 'user'}, {'content': "Answer: A \nExplanation: Paralysis of 3rd, 4th, 6th nerve and involvement of ophthalmic division of 5th nerve → cavernous sinus thrombosis.\nParalysis of 3rd, 4'h, 6th nerve, ophthalmic division of 5th nerve plus optic nerve signs→ orbital apex syndrome.", 'role': 'assistant'}]