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: Biochemistry
[{'content': 'Schilling test is used to test \nSelect and explain. \nA. Vitamin B12 deficiency, B. Vitamin A deficiency, C. Vitamin D deficiency, D. Vitamin B1 deficiency', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]