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': 'Anencephaly is best diagnosed at 12 weeks by : \nSelect and explain. \nA. Serum alpha fetoprotein, B. Ultrasonogram, C. Radiography, D. Amniography', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ultrasonogram', 'role': 'assistant'}]