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: Gynaecology & Obstetrics
[{'content': "OCP's efficiency is reduced by simultaneous use of:a) Rifampicinb) Carbamazepinec) Propranolold) Tricyclic antidepressants \nSelect and explain. \nA. ab, B. a, C. ad, D. bc", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]