**Core Concept**
Sodium (Na+) reabsorption is a critical process in the renal physiology, primarily occurring in the proximal convoluted tubule (PCT) and the thick ascending limb of the loop of Henle. This reabsorption is essential for maintaining proper electrolyte balance, fluid status, and blood pressure.

**Why the Correct Answer is Right**
In the PCT, approximately 65-70% of filtered sodium is reabsorbed through a sodium-glucose cotransporter 2 (SGLT2) mechanism. This cotransporter is driven by the sodium gradient generated by the sodium-potassium pump (Na+/K+-ATPase) in the basolateral membrane of proximal tubular cells. The sodium ions are then reabsorbed into the peritubular capillaries. This mechanism is essential for maintaining the sodium balance in the body.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because, although the descending limb of the loop of Henle is involved in water reabsorption, it is not the primary site for sodium reabsorption.
* **Option B:** This option is incorrect because the distal convoluted tubule (DCT) and collecting ducts are involved in fine-tuning sodium reabsorption and excretion, but they are not the primary sites for maximum sodium reabsorption.
* **Option C:** This option is incorrect because the thick ascending limb of the loop of Henle is involved in sodium reabsorption, but it is not the site with the maximum sodium reabsorption rate compared to the PCT.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the PCT reabsorbs approximately 65-70% of filtered sodium, whereas the DCT and collecting ducts reabsorb or secrete only a small fraction of sodium.

**Correct Answer: A. Proximal Convoluted Tubule (PCT).**