Arteries carry oxygenated blood away from the heart and veins carry deoxygenated blood. that being said, what is unique about the pulmonary arteries and veins

The pulmonary arteries and veins are unique in the type of blood they carry.

the answer to your question is:

c. complementary base-pairing

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.