Difference between the pulmonary artery and the pulmonary vein is that the pulmonary artery has 

Concept: Arteries and veins are blood vessels that help in carrying blood throughout the body of the organism. Arteries help in carrying oxygenated blood throughout the body and veins help in carrying deoxygenated blood.  

The pulmonary artery carries deoxygenated blood (heart to the lungs). The pulmonary vein carries oxygenated blood from (the lungs to the heart). The pulmonary artery arises from the left ventricle of the heart and the pulmonary vein drains into the right atrium of the heart. The walls of the pulmonary artery are thick and elastic in nature and the walls of the pulmonary vein are thin. These arteries also contain semilunar valves whereas veins do not possess these valves. The blood pressure in the pulmonary artery is higher in comparison to the pulmonary vein.

Hence, the correct option is D.