B. Patent ductus arteriosus involves a defect in which the fetal shunt between the aorta and the pulmonary artery fails to close.
Explanation:
Ductus arteriosus is an artery that is function only during fetal stage. It bypasses the non-functional fluid filled lungs while taking flood from the right ventricle . It joins the pulmonary artery to the descending aorta. Normally this artery closes after birth.
If it fails to close then it results in patent ductus arteriousus that causes abnormal blood flow and a part of oxygenated blood flows back into the pulmonary artery from aorta.