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': 'Sex determination in early pregnancy Is done by: \nSelect and explain. \nA. X-rays, B. Amniocentesis, C. Ultrasound, D. Hysteroscopy', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ultrasound', 'role': 'assistant'}]