Anatomy The structure marked A begins to close by what time frame and due to what cause? A Begins to close at 10-15 hours after bih, due to withdrawal of prostaglandins B Begins to close at 10-15 hours after bih, due to expression of prostaglandins C Begins to close 4 weeks after bih, due to fall in oxygen concentration D Begins to close 4 weeks after bih, due to rise in oxygen tension 💡 Explanation The structure marked A begins to close by what time frame and due to what cause? ✓ Correct Answer: A. Begins to close at 10-15 hours after bih, due to withdrawal of prostaglandins