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': 'Allopurinol prevents conversion of - \nSelect and explain. \nA. Hypoxanthine to xanthine, B. Xanthine to hypoxanthine, C. Hypoxanthine to I.M.P, D. All', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Hypoxanthine to xanthine", 'role': 'assistant'}]