**Core Concept**
The Glasgow Outcome Scale (GOS) is a widely used assessment tool for measuring the outcome of patients with traumatic brain injury (TBI). It evaluates the level of recovery and disability after TBI, categorizing patients into five distinct outcomes.

**Why the Correct Answer is Right**
A GOS score of 4 represents a moderate disability. This outcome is characterized by patients who are able to perform daily activities but continue to experience significant cognitive, emotional, or physical impairments. Moderate disability is often associated with patients who have moderate to severe TBI, with some degree of independence but ongoing rehabilitation needs.

**Why Each Wrong Option is Incorrect**
**Option A:** A GOS score of 5 represents good recovery, which implies minimal or no disability, and is not associated with moderate disability.
**Option C:** A GOS score of 3 represents severe disability, which involves significant impairments in daily functioning and a high level of dependence on caregivers.
**Option D:** A GOS score of 2 represents a persistent vegetative state, which is a condition characterized by a lack of responsiveness and awareness, and is not associated with moderate disability.

**Clinical Pearl / High-Yield Fact**
It is essential for healthcare providers to accurately assess and document the GOS score, as it plays a crucial role in determining the prognosis and guiding rehabilitation efforts for patients with TBI.

**✓ Correct Answer: B. Moderate disability**