Which structures take part in the counter-current mechanism?

Human kidneys can produce urine nearly

Which of the following plays a significant role in the production of concentrated urine?

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

Which one of the following animals has a longer loop of Henle?

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: