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: Pathology
[{'content': 'Megaloblastic anaemia occurs due to deficiency of \nSelect and explain. \nA. Niacin, B. Vitamin C, C. Vitamin B1, D. Vitamin B12', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]