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': 'The foetal circulation is first intact and functional, separated from maternal circulation at the age of: \nSelect and explain. \nA. 8 days, B. 12 days, C. 17 days, D. 21 days', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]