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': 'Microtubule formation is inhibited by: \nSelect and explain. \nA. Taxol, B. Vincristine, C. Etoposide, D. Irinotectan', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Vincristine', 'role': 'assistant'}]