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': 'The cutoff 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: Diagnosis of menopause is from classical symptom of hot flush (50%) confirmed by elevated FSH levels to more than 100 mlU/ml and serum estradiol < 20 pg/ml.', 'role': 'assistant'}]