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 earliest diagnosed at : \nSelect and explain. \nA. 6 weeks, B. 10 weeks, C. 14 weeks, D. 18 weeks', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 10 weeks', 'role': 'assistant'}]