This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Gynaecology & Obstetrics
[{'content': 'In normal pregnancy b-Hcg doubles in \nSelect and explain. \nA. 24hours, B. 48hours, C. 72hours, D. 90hours', 'role': 'user'}, {'content': 'Answer: B \nExplanation: With early normal progressing uterine pregnancies, the mean doubling time for serum bhCG levels was approximately 48 hours. The lowest normal value for this increase was 66 percent.Reference: William&;s Obstetrics; 24th edition; Chapter 19; Ectopic Pregnancy', 'role': 'assistant'}]