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
Which of the following are necessary for Niacin synthesis 
Select and explain. 
A. Tryptophan, B. Vitamin B2, C. Vitamin B6, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: 60 mg Tryptophan = 1 mg Niacin
2 x 3 = 6 
Synthesis of vitamin B3 requires B2 and B6.