Final answer:
The major cardiopulmonary change at birth is the closure of the ductus arteriosus, a crucial step in transitioning from fetal to neonatal circulation.
Step-by-step explanation:
Major Cardiopulmonary Change at Birth
One major cardiopulmonary change that occurs in the infant at birth is A) Closure of the ductus arteriosus. After birth, the newborn's lungs inflate with the first breath, reducing pulmonary resistance and prompting the physiological closure of the foramen ovale. As the oxygen content in the blood rises, the smooth muscle in the wall of the ductus arteriosus constricts and eventually closes, a process which is normally completed within the first few days of life. This closure is crucial for properly directing blood flow through the lungs for oxygenation and is a key transition from fetal to neonatal circulation.