This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Intra Uterine Growth Restriction, Intrapaum and Antepaum Fetal Surviellance, Subject name: Gynaecology & Obstetrics
[{'content': 'Diagnosis of Down syndrome at 11 weeks is best assessed by: \nSelect and explain. \nA. Ultrasonography, B. Aminocentesis, C. Chronic villous biopsy, D. Dopper Ultrasound', 'role': 'user'}, {'content': "Answer: C \nExplanation: Confirmatory test for Down's syndrome: 1. First trimester- Chorionic villous sampling(10-13th week) 2. Second trimester - Amniocentesis(16-18th week)", 'role': 'assistant'}]