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 of the following can result in oral contraceptive failure ? \nSelect and explain. \nA. Valproate, B. Rifampicin, C. NSAIDs, D. Ethambutol', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]