This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Contraception, Subject name: Gynaecology & Obstetrics
[{'content': 'What is the minimum dose of ethinyl estradiol in OC pills for contraceptive effect? \nSelect and explain. \nA. 15mcg, B. 20mcg, C. 30mcg, D. 35mcg', 'role': 'user'}, {'content': "Answer: B \nExplanation: For the average patient, the first choice of preparation for contraceptive purposes is a very low estrogen OC (20 mg EE) unless there are other considerations, for example, previous pregnancy while taking the pill.Patients with persistent break-through spotting or bleeding could be offered a pill with the same low estrogen dose, but a more potent progestin, for example, levonorgestrel.Ref: Reference: Novak's gynaecology; 14th edition; Chapter 10; Family planning", 'role': 'assistant'}]