**Core Concept**
During a radical retropubic prostatectomy, bleeding can occur from various sources. The prostate gland is surrounded by a rich network of blood vessels, making it a challenging surgery to perform. The surgeon must be aware of the potential sources of bleeding to minimize complications.

**Why the Correct Answer is Right**
The most troublesome source of bleeding during a radical retropubic prostatectomy is the **dorsal vein complex**. This complex consists of multiple veins that run along the surface of the prostate gland and converge to form a single vein. The dorsal vein complex is a significant source of bleeding because it is a high-pressure system that can bleed profusely if not ligated properly. The surgeon must carefully identify and ligate the dorsal vein complex to prevent excessive bleeding.

**Why Each Wrong Option is Incorrect**
* **Option A:** The **prostatic venous plexus** is another source of bleeding during prostatectomy, but it is not the most troublesome source. This plexus is a network of veins that surrounds the prostate gland and can bleed if not ligated properly.
* **Option B:** The **fascia of Denonvilliers** is a layer of tissue that separates the prostate gland from the rectum. While it can be a source of bleeding, it is not the most troublesome source.
* **Option C:** The **urethra** is not typically a source of bleeding during a radical retropubic prostatectomy, as the surgeon takes care to preserve the urethra during the procedure.

**Clinical Pearl / High-Yield Fact**
To minimize bleeding during a radical retropubic prostatectomy, the surgeon must carefully identify and ligate the dorsal vein complex. This can be achieved by using a technique called "dorsal vein preservation," where the dorsal vein is ligated and divided away from the prostate gland.

**Correct Answer: C. Urethra.**