This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nutrition and Health, Subject name: Social & Preventive Medicine
Niacin is synthesized from:(1994) 
Select and explain. 
A. Tryptophan, B. Tyrosine, C. Methionine, D. Phenyl alanine
A: Tryptophan
Answer: A: Tryptophan 
Explanation: Ans: aRef: Park, 17th ed, p. 420 & 18th ed, p. 446