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
Schilling test is used to test 
Select and explain. 
A. Vitamin B12 deficiency, B. Vitamin A deficiency, C. Vitamin D deficiency, D. Vitamin B1 deficiency
A: Vitamin B12 deficiency
Answer: A: Vitamin B12 deficiency 
Explanation: None