**Core Concept**
Hemiparesis, characterized by weakness on one side of the body, is a common neurological deficit resulting from various cerebrovascular accidents (strokes). The cerebral arteries, including the carotid, middle cerebral artery (MCA), and anterior cerebral artery (ACA), supply blood to the brain and are involved in the pathogenesis of hemiparesis. Understanding the vascular territories and their corresponding clinical manifestations is crucial for diagnosing and managing stroke patients.

**Why the Correct Answer is Right**
Vertebral artery occlusion primarily affects the brainstem, cerebellum, and posterior inferior cerebellar arteries (PICA), leading to symptoms such as dysphagia, dysarthria, ataxia, and nystagmus. The vertebral arteries do not directly supply the motor cortices responsible for hemiparesis, unlike the carotid, MCA, and ACA. Since the vertebral arteries are involved in the posterior circulation of the brain, their occlusion is more likely to result in symptoms such as vertigo, nausea, and loss of coordination, rather than hemiparesis.

**Why Each Wrong Option is Incorrect**
**Option A:** Carotid artery occlusion can cause hemiparesis by occluding the anterior cerebral artery or middle cerebral artery, leading to weakness and paralysis of the contralateral limb.

**Option B:** MCA occlusion is a common cause of hemiparesis due to its extensive supply to the motor and sensory cortices of the contralateral hemisphere. The MCA is responsible for controlling movement on the opposite side of the body.

**Option C:** ACA occlusion can also result in hemiparesis, particularly involving the lower extremities due to the ACA's supply to the motor cortices controlling the legs.

**Clinical Pearl / High-Yield Fact**
In stroke patients, the location and severity of neurological deficits can help identify the affected cerebral artery. A useful mnemonic is "MCA = face, arm, leg" (contralateral facial weakness, arm weakness, and leg weakness) and "ACA = leg" (predominant lower extremity weakness).

**✓ Correct Answer: D. Vertebral artery occlusion**