This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nutrition, Subject name: Medicine
Schilling test is done for ? 
Select and explain. 
A. Vitamin B12 deficiency, B. Folic acid deficiency, C. Vitamin B6 deficiency, D. Vitamin D deficiency
A: Vitamin B12 deficiency
Answer: A: Vitamin B12 deficiency 
Explanation: schilling test to determine whether there is B12 malabsorption and if so where is it occurring Ref Harrison 20th edition pg 78