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': 'Withdraw! bleeding occurs when progestins administered continuously : \nSelect and explain. \nA. Estrogen concentration is sufficient, B. Structural abnormality in the pelvis, C. Associated with endocrine disorder, D. Atrophic endometrium', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Estrogen concentration is sufficient', 'role': 'assistant'}]