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: Medicine
[{'content': "Korsakoff's psychosis is caused by deficiency of vitamin \nSelect and explain. \nA. Vitamin B1, B. Vitamin B2, C. Vitamin C, D. Vitamin D", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]