The concentration of urine depends upon which part of the nephron?

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 glomerular filtrate in the loop of Henle gets concentrated in the descending and then gets diluted in the ascending limbs. Explain.

The concentration of urine depends upon $........$.

Compare the statements $A$ and $B$.
$\text{Statement } A$: When the urine moves through the descending limb,it becomes hypertonic,and as it passes through the ascending limb of Henle's loop,it becomes hypotonic.
$\text{Statement } B$: The descending limb is permeable to sodium ions,while the ascending limb is impermeable to sodium ions.

What is a characteristic feature of the metanephric kidney?