Which of the following is not true based on the cardiovascular changes at birth?

• A. The umbilical vessels degenerate and become fibrous cords.
• B. Rising O₂ levels lead to the constriction of the ductus arteriosus.
• C. The expansion of the lungs results in a sudden decline in resistance in the pulmonary circuit.
• D. The fossa ovalis marks the site of the ductus arteriosus in adults.

Answer: (D)