Final answer:
The correct answer is 3. proximal convoluted tubule and is called obligatory water reabsorption.
Step-by-step explanation:
The correct answer is 3. proximal convoluted tubule and is called obligatory water reabsorption. Reabsorption of water occurs mainly in the proximal convoluted tubule (PCT) of the nephron. The PCT is lined with cells that actively transport ions and create a high concentration of mitochondria in order to produce ATP for the reabsorption process.