**Core Concept**
Hemiplegia refers to the paralysis or weakness of one side of the body, typically resulting from damage to the brain or brainstem. The most common cause of hemiplegia is a stroke, which can occur due to a blockage of blood flow to the brain, known as thrombosis, or a rupture of blood vessels, known as hemorrhage.

**Why the Correct Answer is Right**
Thrombosis of the middle cerebral artery (MCA) is the most common cause of ischemic stroke, accounting for approximately 80% of all strokes. The MCA supplies a significant portion of the cerebral cortex, including areas responsible for motor function, speech, and sensory perception. When the MCA is occluded, it can lead to infarction of the underlying brain tissue, resulting in hemiplegia. The MCA thrombosis can be further classified into two types: anterior cerebral artery (ACA) involvement, which typically results in weakness of the lower limb, and MCA involvement, which typically results in weakness of the upper limb.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not specified, as the question does not provide a clear distractor for Option A.
**Option B:** Anterior cerebral artery (ACA) thrombosis is a less common cause of hemiplegia and typically results in weakness of the lower limb.
**Option C:** Posterior cerebral artery (PCA) thrombosis is a rare cause of hemiplegia and typically results in visual disturbances and ataxia.
**Option D:** Basilar artery thrombosis is a rare cause of hemiplegia and typically results in symptoms affecting multiple cranial nerves and bilateral motor deficits.

**Clinical Pearl / High-Yield Fact**
The FAB (Face, Arm, Speech) examination is a useful tool in assessing patients with suspected hemiplegia, as it can help identify the side and extent of the lesion.

**Correct Answer:** C.