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': 'Macrocytic anaemia is due to deficiency of: \nSelect and explain. \nA. Vit B1, B. Vit B12, C. Vit B2, D. Vit B6', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]