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
Catecholamines are synthesized from: 
Select and explain. 
A. Alanine, B. Glycine, C. Cysteine, D. Tyrosine
D: Tyrosine
Answer: D: Tyrosine 
Explanation: None