The counter-current mechanism operates in:

If Henle's loop were absent from mammalian nephron,which of the following is to be expected?

The function of Henle's loop is

$A$: The final reabsorption of water from urine into blood occurs through the collecting duct of a mammalian nephron,resulting in the production of hyperosmotic urine.
$R$: The loop of Henle is responsible for the formation of a sodium gradient across the depth of the medullary interstitium of a mammalian kidney.

The proximity between Henle's loop and vasa-recta as well as the counter-current in them help in maintaining an ...$A$... in molarity towards the inner medullary interstitium,i.e.,from ...$B$... $mOsmol \ L^{-1}$ in the cortex to about ...$C$... $mOsmol \ L^{-1}$ in the inner medulla. Here $A$,$B$,and $C$ refer to:

Human urine is usually . . . . . . compared to human blood.