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
[{'content': 'A  vasodilator is obtained after decarboxylation of: \nSelect and explain. \nA. Histidine, B. Arginine, C. Tyrosine, D. Glycine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Histidine on decarboxylation gives histamine which is a vasodilator.', 'role': 'assistant'}]