This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anti-Cancer, Subject name: Pharmacology
[{'content': 'Mercaptopurine is \nSelect and explain. \nA. Purine analogue, B. Nucleoside analogue, C. Pyrimidine analogue, D. Anti tumor antibiotics', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ref: Katzung, 14th ed. pg. 960; KDT, 6th ed. pg. 820* Mercaptopurine is synthetic purine used in cancer chemotherapy.* Use: Childhood acute leukemia.', 'role': 'assistant'}]