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': "A young lady taking rifampicin and OCP together become pregnant, most probable cause is \nSelect and explain. \nA. Rifampicin causes hepatic enzyme induction and increase metabolism of OCP's, B. Decreased absorption of OCP's, C. Obstruction of fallopian tubes, D. Increase excretion of OCP's", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]