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': 'Chronic villous sampling is done at : \nSelect and explain. \nA. 4-6 weeks, B. 7-8 weeks, C. 9-11 weeks, D. 12-13 weeks', 'role': 'user'}, {'content': 'Answer: C \nExplanation: 9-11 weeks', 'role': 'assistant'}]