This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fetal circulation, Subject name: Pediatrics
[{'content': 'The ductus aeriosus closes anatomically within:- \nSelect and explain. \nA. Immediately after bih, B. 7 days after bih, C. 4-6 weeks after bih, D. 10 - 21 days after bih', 'role': 'user'}, {'content': 'Answer: D \nExplanation: - Anatomical closure of ductus aeriosus occurs within 10 to 21 days after bih. Occurs by proliferation of its intima cells - Functional closure of ductus aeriosus occurs immediately after bih by smooth muscle contraction which occurs as a result of increase in oxygen saturation.', 'role': 'assistant'}]