**Core Concept**
Gitelman's syndrome is a rare genetic disorder characterized by **hypokalemic alkalosis**, **hypomagnesemia**, and **hypocalciuria**, resulting from a defect in the **thiazide-sensitive sodium-chloride cotransporter** in the distal convoluted tubule.

**Why the Correct Answer is Right**
The correct answer is related to the effect of **thiazide diuretics**, which act by inhibiting the **sodium-chloride cotransporter** in the distal convoluted tubule, leading to increased excretion of sodium and chloride, resulting in **hypokalemia** and **metabolic alkalosis**.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it does not relate to the pathophysiology of Gitelman's syndrome.
**Option B:** Incorrect as it is not associated with the **thiazide-sensitive sodium-chloride cotransporter**.
**Option C:** Incorrect because it is related to a different mechanism.

**Clinical Pearl / High-Yield Fact**
Remember that Gitelman's syndrome and **Bartter syndrome** are both characterized by **hypokalemic alkalosis**, but they differ in their urinary calcium excretion, with Gitelman's syndrome having **hypocalciuria**.

**Correct Answer:** D. Thiazide diuretics.