"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.

C. the pulmonary artery and vein; they would have to be switched.

Explanation:

The pulmonary artery leaves the heart with deoxygenated blood while the pulmonary vein enters the heart with oxygenated blood from the lungs.

The pulmonary artery and pulmonary vein are the only ones that work in the opposite way from the rest of the veins and arteries in the body. The rest of the arteries have oxygenated blood and the rest of the veins have deoxygenated blood.

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