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: Pharmacology
Serotonin can be synthesized from : 
Select and explain. 
A. Tryptophan, B. Tyrosine, C. Dopa, D. Epinephrine
A: Tryptophan
Answer: A: Tryptophan 
Explanation: None