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': 'By which day after feilization, is placental circulation established : \nSelect and explain. \nA. 11th day, B. 13th day, C. 15th day, D. 17th day', 'role': 'user'}, {'content': 'Answer: D \nExplanation: 17th day', 'role': 'assistant'}]