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': 'Diagnosis of Down syndrome at 11 weeks in the best assessed by \nSelect and explain. \nA. Ultrasonography, B. Aminocentesis, C. Chorionic villous biopsy, D. Doppler ultrasound', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans is c i.e. Chorionic viii biopsy', 'role': 'assistant'}]