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': 'Contraceptive pill with least failure rate : \nSelect and explain. \nA. Sequential pill, B. Mini pill, C. Combined pill, D. None', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Combined pill', 'role': 'assistant'}]