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': 'Which one of the following alkaloids is used as anti–cancer agent ? \nSelect and explain. \nA. Vincristine, B. Papaverine, C. Ephedrine, D. Atropine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]