**Core Concept**
The anterior cerebral artery (ACA) supplies the medial surface of the brain, including the medial frontal lobe, the paracentral lobule, and the anterior part of the corpus callosum. Occlusion of the ACA can lead to ischemia in these areas, resulting in various neurological deficits.

**Why the Correct Answer is Right**
Occlusion of the ACA can cause contralateral lower limb weakness or paralysis due to involvement of the motor cortex and the corticospinal tracts. The ACA also supplies the anterior part of the corpus callosum, which is involved in inter-hemispheric communication. Therefore, ACA occlusion can lead to disconnection between the two hemispheres, resulting in a condition known as "magnetic apraxia," where the patient has difficulty with inter-hemispheric transfer of information.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because occlusion of the posterior cerebral artery (PCA) would primarily affect the occipital lobe, leading to visual field defects.
* **Option B:** This option is incorrect because occlusion of the middle cerebral artery (MCA) would primarily affect the lateral surface of the brain, leading to upper limb weakness, facial weakness, and language deficits.
* **Option C:** This option is incorrect because occlusion of the vertebral artery would primarily affect the brainstem and cerebellum, leading to symptoms such as ataxia, dysarthria, and cranial nerve deficits.

**Clinical Pearl / High-Yield Fact**
The ACA is often affected in conditions such as Moyamoya disease, a rare disorder characterized by progressive stenosis or occlusion of the internal carotid artery and its branches, leading to ischemia in the anterior circulation.

**Correct Answer: D. Contralateral lower limb weakness.**