**Core Concept:** The nephron is the functional unit of the kidney responsible for filtering blood, reabsorbing essential substances, and excreting waste products. In the nephron, reabsorption occurs mainly in the proximal convoluted tubule (PCT), distal convoluted tubule (DCT), and collecting duct (CD).

**Why the Correct Answer is Right:** In the nephron, reabsorption occurs primarily in the PCT, DCT, and CD. Option C (loop of Henle) is incorrect as the majority of reabsorption occurs in the ascending limb (AL) and descending limb (DL) of the loop of Henle, not the loop itself.

**Why Each Wrong Option is Incorrect:**

A. Option A (proximal straight tubule) is incorrect because it is a part of the PCT where reabsorption occurs, not least.
B. Option B (corpuscle) is incorrect as it refers to the glomerulus, not a specific nephron segment involved in reabsorption.
D. Option D (distal convoluted tubule) is incorrect as it is a part of the DCT, where reabsorption occurs, not least.

**Clinical Pearl / High-Yield Fact:** Understanding nephron function and reabsorption sites is crucial for understanding renal function, electrolyte homeostasis, and the interpretation of clinical laboratory tests. This knowledge is vital for medical students, residents, and practicing physicians to diagnose and manage renal disorders effectively.