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

In vertebrates,the ability to produce concentrated urine is generally associated with the ............ .

We can produce a concentrated urine. This is facilitated by a special mechanism. Identify the mechanism.

Which of the following statements is correct?

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

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