**Core Concept**
In patients with cirrhosis of the liver, portal hypertension leads to the formation of varices and splenomegaly. The increased pressure in the portal vein causes blood to be diverted through collateral pathways, including the hepatic veins, which are under increased pressure. This results in the formation of thrombi in these veins.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of portal hypertension and the formation of hepatic venous thrombosis. The hepatic veins are under increased pressure due to portal hypertension, leading to stasis and clot formation. The increased pressure in the hepatic veins is caused by the diversion of blood through collateral pathways, including the splenic and mesenteric veins.

*Option A:* **Option A:** is incorrect because it refers to the hepatic artery, which is not directly related to the formation of venous thrombosis in cirrhosis.

*Option B:* **Option B:** is incorrect because it refers to the portal vein, which is the site of thrombosis in some cases, but not the most common site in patients with cirrhosis.

*Option D:* **Option D:** is incorrect because it refers to the superior mesenteric vein, which is a collateral pathway that may form to bypass the portal vein, but is not the site of venous thrombosis in cirrhosis.

**Clinical Pearl / High-Yield Fact**
The formation of hepatic venous thrombosis in cirrhosis is a complication that can lead to hepatic failure and death if not treated promptly. It is essential to recognize the signs and symptoms of hepatic venous thrombosis, such as abdominal pain and ascites, and to perform imaging studies to confirm the diagnosis.

**Correct Answer:** C. The hepatic veins are the site of venous thrombosis in patients with cirrhosis of the liver.