**Core Concept**
Hypercalcemia is a condition characterized by elevated serum calcium levels, which can be caused by various factors such as hyperparathyroidism, malignancy, or vitamin D toxicity. Treatment options aim to reduce calcium levels and alleviate symptoms.

**Why the Correct Answer is Right**
To manage hypercalcemia, medications that reduce calcium absorption, promote its excretion, or inhibit its release from bone are used. **Bisphosphonates**, such as pamidronate, work by inhibiting osteoclast-mediated bone resorption, thereby reducing calcium release from bone. **Calcitonin**, a hormone produced by the thyroid gland, decreases osteoclast activity and promotes calcium deposition in bone. **Loop diuretics**, like furosemide, increase calcium excretion in the urine by enhancing its reabsorption in the distal tubules.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because **Vitamin D** can actually exacerbate hypercalcemia by increasing calcium absorption from the gut.
**Option B:** This option is incorrect because **Thiazide diuretics** can increase calcium reabsorption in the distal tubules, leading to elevated serum calcium levels.
**Option C:** This option is incorrect because **Corticosteroids** are not a primary treatment for hypercalcemia; they may be used in cases of hypercalcemia caused by malignancy, but are not a direct treatment for reducing calcium levels.

**Clinical Pearl / High-Yield Fact**
In cases of hypercalcemia, it's essential to consider the underlying cause and tailor treatment accordingly. For example, if hypercalcemia is caused by a malignancy, bisphosphonates may be used in conjunction with other treatments like glucocorticoids or denosumab.

**Correct Answer: A. Vitamin D. Vitamin D**