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
Which of the following is a stimulus for closure of ductus arteriosus? 
Select and explain. 
A. Increased O2 tension, B. Hypoxia, C. Prematurity, D. Hypercapnia
A: Increased O2 tension
Answer: A: Increased O2 tension 
Explanation: a. Increased O2 tension(Ref: Nelson's 20/e p 2162)In the course of several days after birth, the high arterial Po2 constricts and eventually closes the ductus arteriosus, which eventually becomes the ligamentum arteriosum