**Core Concept**
Couinaud's classification is a system used to divide the liver into segments based on its vascular supply and drainage. This classification is essential in liver surgery, transplantation, and interventional radiology. The classification divides the liver into eight segments, each with its own hepatic artery, portal vein, and bile duct.

**Why the Correct Answer is Right**
The correct answer is because Couinaud's classification divides the liver into eight segments. This classification is based on the hepatic veins, which are used as landmarks to separate the liver into segments. The segments are numbered from I to VIII, with segment I being the caudate lobe and segment VIII being the superior posterior segment. Each segment has its own specific blood supply, drainage, and function.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because Couinaud's classification does not divide the liver into four segments.
* **Option B:** This option is incorrect because the liver is not divided into five segments according to Couinaud's classification.
* **Option C:** This option is incorrect because the liver is not divided into nine segments according to Couinaud's classification.
* **Option D:** This option is incorrect because the liver is not divided into six segments according to Couinaud's classification.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that Couinaud's classification is a fundamental concept in liver surgery and interventional radiology. Understanding this classification is crucial for accurate diagnosis and treatment of liver diseases.

**Correct Answer:** C. 8.