This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Gynaecology & Obstetrics
[{'content': 'Ligamentum teres is formed after : \nSelect and explain. \nA. Obliteration of the umbilical vein, B. Obliteration of the ductus venous, C. Obliteration of the ductus aeriosus, D. Obliteration of the hypogastric aery', 'role': 'user'}, {'content': "Answer: A \nExplanation: Intraabdominal remnants of Umbilical vein forms the ligamentum teres. The more distal poions of the hypogastric aeries,which course from the level of the bladder along the abdominal wall to the umbilical ring and into the cord as umbilical aeries,undergo atrophy and obliterates within 3-4 days after bih, becomes umbilical ligaments. The Ductus venosus constricts by 10-96 hours after bih and is anatomically closed by 2-3 weks, resulting in the formation of ligamentum venosum. Reference: William's Textbook of Obstetrics 4th edition, page 137", 'role': 'assistant'}]