Then what is the function of option c

The proximal convoluted tubule (option C) is primarily responsible for the reabsorption of most of the useful substances from the glomerular filtrate back into the blood. This includes about 65% of the filtered water, sodium ions, chloride ions, bicarbonate ions, and nearly 100% of filtered glucose and amino acids. It also plays a role in the secretion of some waste products and drugs into the filtrate.