After birth, the ductus arteriosus constricts due to rising oxygen levels and eventually becomes the:

1. All three fetal circulatory shunts must close after birth for the neonatal circulation to function properly. 2. Increased blood oxygen concentration after the first breaths causes the ductus arteriosus specifically to constrict. 3. This constricted structure eventually becomes a permanent ligament. 4. Ligamentum venosum and Fossa ovalis are both different figures a reader might guess from memory, but neither matches the specific figure given here. 5. Round ligament is also incorrect for the same reason: it does not match the specific figure given here. 6. That structure is the ligamentum arteriosum, distinct from the ligamentum venosum (from the ductus venosus) and the fossa ovalis (from the foramen ovale). _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 28 "Development and Inheritance", p.1349 §Circulatory Adjustments_