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
The amino acid from which niacin is synthesized is: 
Select and explain. 
A. Tyrosine, B. Threonine, C. Tryptophan, D. Histidine
C: Tryptophan
Answer: C: Tryptophan 
Explanation: None