**Core Concept**
The posterior columns of the spinal cord are responsible for transmitting sensations of proprioception, vibration, and fine touch from the lower limbs to the brain. This is mediated by the dorsal columns, specifically the fasciculus gracilis and fasciculus cuneatus, which convey information from the lower and upper limbs, respectively.

**Why the Correct Answer is Right**
Vitamin B12 deficiency leads to subacute combined degeneration (SACD) of the spinal cord, which primarily affects the posterior columns. This is because vitamin B12 is essential for the synthesis of myelin, the fatty substance that surrounds and protects nerve fibers. In SACD, the myelin sheaths of the posterior columns degenerate, resulting in loss of proprioception, vibration, and fine touch sensations in the lower limbs. The dorsal columns are particularly vulnerable to vitamin B12 deficiency due to their high metabolic demands.

**Why Each Wrong Option is Incorrect**
**Option A:** Vitamin A deficiency primarily affects the retina and vision, leading to night blindness, not posterior column sensations.
**Option C:** Vitamin C deficiency causes scurvy, which affects collagen synthesis and leads to connective tissue disorders, but not posterior column sensations.
**Option D:** Vitamin D deficiency can cause rickets and osteomalacia, which affect bone mineralization, but not posterior column sensations.

**Clinical Pearl / High-Yield Fact**
Remember the classic association between vitamin B12 deficiency and subacute combined degeneration of the spinal cord, which can lead to loss of posterior column sensations in the lower limbs.

**Correct Answer:**
✓ Correct Answer: B. Vitamin B12 deficiency