"artery" and "vein" are defined by whether they leave or enter the heart. if they were defined by whether they carried oxygenated or deoxygenated blood, we would have to change the name(s) of
a. the hepatic portal vein to a hepatic portal artery.
b. the hepatic and renal systems; they would have to be switched.
c. the pulmonary artery and vein; they would have to be switched.
d. the coronary artery and vein; they would have to be switched.
e. none, since the aorta and vena cava do not have "artery" and "vein" in their name.