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

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 Henle's loop is

What is the counter current mechanism?

Describe the counter-current mechanism.

Human urine is usually . . . . . . compared to human blood.