A 26-year-old woman at 38-weeks of gestation comes to the hospital in labour She has been having an uncomplicated pregnancy so far. All her prenatal testing showed no abnormalities In utero, the fetus has a specialised type of circulation of blood from the mother to the fetus. 
While in utero, which of the following structures shunts blood from the pulmonary artery to the descending aorta?
Ductus arteriosus
Ductus venosum
Foramen ovale
Ligamentum arteriosum