Explanation:

Introduction:
Veins are blood vessels that carry blood towards the heart. They are responsible for transporting deoxygenated blood back to the heart, except for one exception.

Veins and Blood Circulation:
Veins form an essential part of the circulatory system, working alongside arteries and capillaries. Arteries carry oxygenated blood away from the heart to various tissues and organs, while veins carry deoxygenated blood back to the heart.

Difference between Arteries and Veins:
One key difference between arteries and veins is the oxygen content of the blood they carry. Arteries carry oxygenated blood, while veins carry deoxygenated blood. However, there is one exception to this rule.

The Exception:
The pulmonary vein is the only vein in the body that carries oxygenated blood. This vein carries blood from the lungs back to the heart. After oxygen enters the bloodstream through the process of respiration in the lungs, it binds to red blood cells, resulting in oxygenated blood. This oxygenated blood is then transported from the lungs to the heart through the pulmonary vein.

Other Veins:
The other veins mentioned in the options are as follows:

- Hepatic vein: The hepatic vein carries deoxygenated blood from the liver to the inferior vena cava, which then transports blood back to the heart.
- Hepatic portal vein: The hepatic portal vein carries nutrient-rich but deoxygenated blood from the digestive organs (such as the stomach, intestines, and spleen) to the liver for processing before it reaches the heart.
- Renal vein: The renal vein carries deoxygenated blood from the kidneys to the inferior vena cava.

In summary, the pulmonary vein is the only vein that carries oxygenated blood in the body. All other veins, including the hepatic vein, hepatic portal vein, and renal vein, carry deoxygenated blood back to the heart.