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': 'The amino acid from which niacin synthesized is: \nSelect and explain. \nA. Tyrosine, B. Tryptophan, C. Threonine, D. Histidine', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]