Which determines the abiltiy of a mammal to concentrate its urine

Which feature enables the mammalian kidney to concentrate urine in the medullary region?

How is concentrated urine formed?

Which animals have the ability to produces concentrated urine

The urine excreted by mammals is

Assertion :- Mammals have the ability to produce a concentrated urine. Reason :- Counter current mechanism occurs in vasa recta and Henle's loop.

Assertion :- Mammals have the ability to produce a concentrated urine. Reason :- Counter current mechanism occurs in vasa recta and Henle's loop.

Which of the following animal has the least concentrated urine relative to its blood plasma?