Which adaptation is shown by desert organisms?

Which of the following statements about the reabsorption process in Henle's loop are correct?
$(a)$ The descending limb of Henle's loop is permeable to water but almost impermeable to electrolytes.
$(b)$ Urine gets concentrated in Henle's loop.
$(c)$ Reabsorption of $Na^+$ and water takes place in Henle's loop.
$(d)$ Active or passive transport of electrolytes occurs in the ascending limb of Henle's loop.
Choose the correct answer from the options given below:

The function of the loop of Henle is:

Mention the substances that exit from the tubules in order to maintain a concentration gradient in the medullary interstitium.

Medullary gradient is mainly developed due to

Which of the following factors is responsible for the formation of concentrated urine?