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': 'Best time for detecting chorionicity twin pregnancy on USG Is: \nSelect and explain. \nA. 8-12 weeks, B. 10-14 weeks, C. 14-18 weeks, D. 16-24 weeks', 'role': 'user'}, {'content': 'Answer: B \nExplanation: <p> Chorionicity of the placenta is best diagnosed by ultrasound at 10-13 weeks of gestation. Reference:DC Dutta&;s textbook of obstetrics,8th edition,page no;237 <\\p>', 'role': 'assistant'}]