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': 'Basilar insufficiency shows: \nSelect and explain. \nA. Ptosis, B. Blurred vision, C. Diplopia, D. VI nerve weakness', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Ptosis', 'role': 'assistant'}]