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
Which of the following is the precursor of adrenaline and noradrenaline? 
Select and explain. 
A. Phenylalanine, B. Tyrosine, C. Tryptophan, D. None of the above
B: Tyrosine
Answer: B: Tyrosine 
Explanation: Tyrosine is the contributing amino acid for the formation of thyroxine, tri-iodothyronine, epinephrine, norepinephrine, dopamine and melanin