**Core Concept**
The underlying principle being tested is the metabolism and excretion of bilirubin in the context of jaundice, specifically the role of **urobilinogen**. Jaundice is characterized by elevated levels of **bilirubin** in the blood, which can be due to pre-hepatic, hepatic, or post-hepatic causes. **Urobilinogen** is a colorless by-product of bilirubin reduction, produced by intestinal bacteria.

**Why the Correct Answer is Right**
The correct answer choice is related to the complete obstruction of the bile duct, which prevents **bilirubin** from reaching the intestines. As a result, no **urobilinogen** is formed, and consequently, none is absorbed back into the bloodstream to be excreted by the kidneys into the urine. This indicates a post-hepatic cause of jaundice, where the flow of bile into the intestine is blocked.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it does not directly relate to the absence of urobilinogen in urine.
**Option B:** Incorrect as it might relate to liver dysfunction but does not specifically explain the absence of urobilinogen.
**Option C:** Incorrect because it is unrelated to the metabolic pathway of bilirubin to urobilinogen.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the presence or absence of **urobilinogen** in urine can help differentiate between types of jaundice. Its absence suggests a complete obstruction of the bile duct, preventing bilirubin from reaching the intestines where it would be converted to urobilinogen.

**Correct Answer:** D. Complete obstruction of bile duct.