The function of Henle's loop is

The increase in osmolarity from outer to inner medullary interstitium is maintained due to:
$(i)$ Close proximity between Henle's loop and vasa recta
$(ii)$ Counter current mechanism
$(iii)$ Selective secretion of $HCO_{3}^{-}$ and hydrogen ions in $PCT$
$(iv)$ Higher blood pressure in glomerular capillaries

What does the following figure represent?

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

The vasa recta are tubular capillaries around the ........

If the $Loop$ $of$ $Henle$ is absent from the mammalian nephron,which of the following is likely to occur?