This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vitamins and Minerals, Subject name: Biochemistry
Which of the following vitamin is metabolically produced by the body? 
Select and explain. 
A. Biotin, B. Vitamin K, C. Niacin, D. Pyridoxine
C: Niacin
Answer: C: Niacin 
Explanation: Essential amino acid tryptophan can be conveed into Niacin (B3) in our body (60 mg tryptophan = 1 mg Niacin). As, it can be synthesised in the body by metabolism, strictly speaking, Niacin is not a Vitamin.