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': 'In the early pregnancy, the doubling time of HCG concentrations in plasma is : \nSelect and explain. \nA. 12 hours, B. 48 hours, C. 72 hours, D. 96 hours', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 48 hours', 'role': 'assistant'}]