**Core Concept:** Couinaud's classification is a system for dividing the liver into functional segments based on blood supply and biliary drainage.

Couinaud's classification is named after French surgeon Clouston Couinaud who first described this system in 1957. It divides the liver into eight segments, each with a unique blood supply and biliary drainage pattern. This classification is essential for understanding surgical anatomy and liver transplantation.

**Why the Correct Answer is Right:**

Correct Answer: D. Segment IV

Segment IV of the liver is classified as segment IV. This segment is also known as the "right lobe" and is characterized by its right lateral segment, which receives blood supply from the right hepatic artery and drains into the right portal vein and right hepatic duct.

**Why Each Wrong Option is Incorrect:**

A. This answer is incorrect because Segment IV is the right lobe of the liver, not a separate segment.
B. Segment II is the most inferior segment, not IV.
C. Segment V is located posterior to the inferior vena cava, not IV.

**Clinical Pearl / High-Yield Fact:**

Understanding Couinaud's classification is crucial for surgeons, radiologists, and transplantologists as it helps in identifying specific liver segments, planning surgical procedures, and interpreting liver imaging studies.