This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Molecular Genetics, Subject name: Biochemistry
Serotonin is derived from - 
Select and explain. 
A. Tyrosine, B. Phenylalanine, C. Alanine, D. Tryptophan
D: Tryptophan
Answer: D: Tryptophan 
Explanation: Ans. is 'd' Le., Tryptophan