**Core Concept**
The question requires understanding of the metabolic pathway of vitamin D, specifically the conversion of cholecalciferol (Vitamin D3) to its active form, 1,25-dihydroxycholecalciferol (1,25(OH)2D3). This process involves two hydroxylation reactions, one in the liver and the other in the kidneys.

**Why the Correct Answer is Right**
The first hydroxylation occurs in the liver, where cholecalciferol is converted to 25-hydroxycholecalciferol (25(OH)D3) by the enzyme 25-hydroxylase. This step is essential for the formation of the active hormone. The second hydroxylation takes place in the kidneys, where 25(OH)D3 is converted to 1,25(OH)2D3 by the enzyme 1α-hydroxylase. This enzyme is regulated by parathyroid hormone (PTH), calcium levels, and phosphate levels.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the first hydroxylation occurs in the liver, not in the skin (where cholecalciferol is initially synthesized).
**Option B:** Incorrect because the second hydroxylation occurs in the kidneys, not in the liver.
**Option C:** Incorrect because the conversion of cholecalciferol to 1,25(OH)2D3 is not the first step in vitamin D metabolism.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the active form of vitamin D, 1,25(OH)2D3, is produced in the kidneys and plays a crucial role in maintaining calcium and phosphate homeostasis.

**Correct Answer: C. Skin.