This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
[{'content': 'The only water-soluble vitamin stored in the body \nSelect and explain. \nA. B1, B. B2, C. B6, D. B12', 'role': 'user'}, {'content': "Answer: D \nExplanation: Cobalamin is synthesized solely by microorganisms. Ruminants obtain cobalamin from the foregut, but the only source for humans is the food of animal origin, e.g., meat, fish, and dairy products. Body stores are of the order of 2-3 mg, sufficient for 3-4 years if supplies are completely cut off. Ref: Harrison's Principles of Internal Medicine; 19th edition; Chapter 128 Megaloblastic Anemias", 'role': 'assistant'}]