Cuboidal epithelium with a brush border is a characteristic of which of the following?

In the renal tubule,the reabsorption of chloride ions from the glomerular filtrate occurs by:

The proximal convoluted tubule has a brush border which is due to

Reabsorption of useful substances from the glomerular filtrate occurs in the:

$A :$ Tubular secretion is of considerable importance in marine teleost fishes.
$R :$ These have aglomerular kidney,$i.e.$,no filtration occurs and tubular secretion is the only way of excretion.

Reabsorption in the tubules of nephrons occurs by the process of