**Core Concept**
Klatskin's tumor is a rare, aggressive type of cholangiocarcinoma that occurs at the junction of the right and left hepatic bile ducts. It is a type of malignant tumor that arises from the epithelial lining of the bile ducts.

**Why the Correct Answer is Right**
Klatskin's tumor is characterized by the presence of a tumor at the hepatic duct bifurcation, which can cause obstructive jaundice and liver dysfunction. The tumor is often large and can compress the bile ducts, leading to bile duct dilation and potentially causing cholangitis. Surgical resection is the primary treatment for Klatskin's tumor, but it is often challenging due to the tumor's location and the need to preserve the hepatic ducts.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specifically describe a tumor at the hepatic duct bifurcation.
* **Option B:** This option is incorrect because it refers to a different type of bile duct tumor that occurs in the distal common bile duct.
* **Option C:** This option is incorrect because it refers to a benign condition characterized by the dilation of the bile ducts.

**Clinical Pearl / High-Yield Fact**
Klatskin's tumor is often associated with risk factors such as primary sclerosing cholangitis, chronic biliary tract disease, and hepatitis B or C infection. A high index of suspicion is necessary to diagnose this rare and aggressive tumor.

**Correct Answer: C. Bile duct carcinoma at the hepatic duct bifurcation.**