**Core Concept:** Pelvic fractures are serious injuries that can lead to disruption of the urinary, genital, and gastrointestinal systems. Urinary retention in these patients is a dangerous sign indicating potential urethral and bladder involvement.

**Why the Correct Answer is Right:** The correct answer, D, refers to the bladder involvement in a pelvic fracture. When a pelvic fracture occurs, the injury can disrupt the structures within the pelvis, including the bladder, causing it to become compressed or obstructed, leading to urinary retention. This issue, along with urethral disruption, is a serious complication and requires urgent evaluation and treatment.

**Why Each Wrong Option is Incorrect:**

A. Urethral bleeding is a separate yet related complication of pelvic fractures. However, the question specifically mentions the patient is unable to pass urine, making this option less relevant.

B. Urethral bleeding (Option A) is a potential complication of pelvic fractures, but the question focuses on the inability to pass urine. This option does not address the primary concern of urinary retention.

C. Urethral injury (Option A) is also a complication of pelvic fractures but, as previously mentioned, the patient is unable to pass urine. This option does not address the primary concern.

**Clinical Pearl:** When evaluating patients with suspected pelvic fractures, it is crucial to assess for associated complications such as urethral and bladder involvement, as these can lead to serious complications and require immediate medical attention.

**Correct Answer:** D. Urethral and bladder involvement in a pelvic fracture can lead to urinary retention, which is a serious complication and requires urgent evaluation and treatment.