**Core Concept**
Bilirubin is a yellow compound that occurs in the normal catabolic pathway that breaks down heme in red blood cells. It is water-insoluble and therefore cannot be excreted in the urine.

**Why the Correct Answer is Right**
Bilirubin is conjugated in the liver before being excreted into the bile. The conjugated bilirubin is then stored in the gallbladder and released into the small intestine, where it is converted to urobilinogen by the action of intestinal bacteria. Urobilinogen is then reabsorbed into the bloodstream and either excreted in the urine or converted back to bilirubin and excreted in the feces. Since bilirubin is water-insoluble, it is not filtered by the kidneys and therefore not present in the urine.

**Why Each Wrong Option is Incorrect**
* **Option A:** Incorrect, as it does not provide a valid reason for bilirubin's absence in urine.
* **Option B:** Incorrect, as it suggests that bilirubin is excreted in the urine, which is not the case.
* **Option C:** Incorrect, as it implies that bilirubin is water-soluble, which is not true.

**Clinical Pearl / High-Yield Fact**
Bilirubin is a lipophilic compound that requires conjugation in the liver to become water-soluble. This process is essential for its excretion in the bile and subsequent conversion to urobilinogen in the intestine.

**Correct Answer: D.**