Reabsorption of glucose from the glomerular filtrate in the kidney tubule is carried out by

During urine formation,the tubular cells secrete substances like ........... into the filtrate.

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

Brush-bordered epithelium (microvilli-bearing) is found in:

$A :$ 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.

In which segment of the nephron does the conditional reabsorption of $Na^+$ and water occur?