The correct answer is b) proximal tubule.
Selective reabsorption primarily occurs in the proximal tubule of the nephron. This segment is responsible for reabsorbing approximately 65-70% of filtered water, sodium, and various other solutes. The proximal tubule features numerous microvilli, which increase the surface area available for absorption, and specialized transport mechanisms to facilitate the process of reclaiming important substances from the filtrate back into the bloodstream.
Other structures, such as the loop of Henle and distal tubule, also contribute to reabsorption but to a lesser extent compared to the proximal tubule. For instance, while the collecting duct can fine-tune the final urine concentration under hormonal control, most of the selective reabsorption has already taken place by the time the filtrate reaches this point.