This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Menopause and HRT, Subject name: Gynaecology & Obstetrics
[{'content': 'The cut-off point of serum estrogen level for the diagnosis of ovarian failure: \nSelect and explain. \nA. 10 pg/mL, B. 20 pg/mL, C. 30 pg/mL, D. 40 pg/mL', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ovarian failure diagnosis history of amenorrhea <35 years of age FSH>40mIU/L Estrogen>20pg/ml karyotype anomaly organ specific humoral antibody ovarian biopsy D.C.DUTTA&;S TEXTBOOK OF GYNAECOLOGY,g no:463,6th edition', 'role': 'assistant'}]