**Core Concept**
The Couinaud's segmental nomenclature is a classification system used to divide the liver into eight distinct segments based on the distribution of the hepatic veins and portal vein. This system is crucial for liver surgery, transplantation, and understanding liver anatomy.

**Why the Correct Answer is Right**
The Couinaud's classification is based on the concept that the liver receives blood from two main sources: the portal vein, which carries oxygen-depleted blood from the digestive tract, and the hepatic veins, which drain oxygen-rich blood from the liver. By segmenting the liver based on the distribution of these vessels, surgeons can better understand the liver's anatomy and avoid damaging vital structures during surgery. The hepatic veins are divided into three main branches, while the portal vein divides into five main branches, which together form the basis for the eight liver segments.

**Why Each Wrong Option is Incorrect**
**Option B:** Biliary ducts are not a primary factor in the Couinaud's classification, as they do not directly influence the segmentation of the liver.
**Option C:** While the portal vein is a key component of the Couinaud's classification, the biliary ducts are not used to segment the liver.
**Option D:** The hepatic artery is not a primary factor in the Couinaud's classification, as it does not directly influence the segmentation of the liver.

**Clinical Pearl / High-Yield Fact**
It is essential for surgeons to understand the Couinaud's classification to avoid damaging vital structures during liver surgery, such as the hepatic veins, portal vein, and bile ducts. A thorough knowledge of liver anatomy is crucial for successful liver transplantation and surgical outcomes.

**✓ Correct Answer: A. Hepatic veins and portal vein**