This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous (Structure & Function of Proteins), Subject name: Biochemistry
[{'content': 'Precursor of norepinephrine - \nSelect and explain. \nA. Tryptophan, B. Tyrosine, C. Methionine, D. Asparagine', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e.. Tyrosine", 'role': 'assistant'}]