This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Pediatrics
Anatomical closure of ductus aeriosus occurs at ________ 
Select and explain. 
A. Bih, B. 3-4 days, C. 10-21 days, D. 10-15 hours
C: 10-21 days
Answer: C: 10-21 days 
Explanation: Ductus aeriosus is functionally closed at 10-15 hours after bih and then anatomical closure occurs at 10-12 days. Ref: Ghai essential pediatrics 9th edition Pgno: 400