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
[{'content': 'Which of the following is the precursor for adrenaline and thyroxine synthesis? \nSelect and explain. \nA. Phenylalanine, B. Tyrosine, C. Tryptophan, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Harper – 267, 446\nTyrosine is the precursor for triiodothyronine and thyroxine. It is also an immediate precursor for the catecholamines (adrenaline) and tyrosine hydroxylase is the rate limiting enzyme in the catecholamine biosynthesis.', 'role': 'assistant'}]