## Core Concept
The common bile duct (CBD) is a vital structure in the biliary system, formed by the junction of the right and left hepatic ducts. It plays a crucial role in transporting bile from the liver and gallbladder to the small intestine for fat digestion. The CBD's anatomical and physiological characteristics are essential for understanding various hepatobiliary disorders.

## Why the Correct Answer is Right
The correct answer, ., implies that one of the statements provided about the common bile duct is not true. To address this, let's evaluate each option based on known facts about the CBD.

## Why Each Wrong Option is Incorrect
- **Option A:** Typically, the common bile duct is about 7-9 cm long and 5-10 mm in diameter. If option A states a fact within this range or a recognized characteristic, it would be correct, and its exclusion implies it's not the incorrect statement.
- **Option B:** The CBD usually joins the main pancreatic duct to form the ampulla of Vater, which then empties into the second part of the duodenum. This is a well-established anatomical fact. If option B contradicts this, it's incorrect.
- **Option C:** If option C provides a recognized feature or function of the CBD, such as its role in bile transport or its relationship with surrounding structures, and it's accurate, then it's not the answer.
- **Option D:** Given as the correct answer, implying the other options might have accurate statements about the CBD.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the **common bile duct** runs closely with the **hepatic artery** and the **portal vein** within the hepatoduodenal ligament. Obstruction of the CBD can lead to jaundice and changes in liver function tests, making its anatomy and physiology critical for clinical diagnosis and management.

## Correct Answer: D.