In the given diagram,what are the regions $P, Q,$ and $R$?
$P \quad\quad Q \quad \quad R$

Given below are two statements with respect to counter current mechanism.
$Statement-I$: Tissue fluid around the descending limb of Henle's loop becomes concentrated, during the counter current mechanism.
$Statement-II$: Water moves out from the descending limb of Henle's loop into the tissue fluid by osmosis.
In the light of the above statements, select the correct option from the codes given below:

Which feature enables the mammalian kidney to concentrate urine in the medullary region?

Which part of the nephron plays a significant role in the maintenance of high osmolarity of the interstitial fluid?

If the kidneys fail to reabsorb water,what effect will be observed on the tissues?

Urine is concentrated in which part of the nephron?