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': 'Mechanism of action of oral contraceptives containing ethinyl oestradiol and a progesterone is : \nSelect and explain. \nA. Inhibiting ovulation, B. Inhibiting the implantation, C. Thickening of cervical mucus, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Inhibiting ovulation', 'role': 'assistant'}]