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': 'The most common cause of pulsating exophthalmos is: \nSelect and explain. \nA. Orbital varices, B. Neurofibromatosis, C. Cavernous haemangioma, D. Caroticocavernous fistula', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. Caroticocavernous fistula', 'role': 'assistant'}]