Human kidneys can produce urine about four times as concentrated as the initial filtrate. Evaluate the Assertion and Reason.

• Assertion (A): Human kidneys can produce urine that is about four times more concentrated than the glomerular filtrate.
• Reason (R): The counter current arrangement of the loop of Henle and vasa recta maintains an osmolarity gradient in the medullary interstitium, from about 300 mOsmol L⁻¹ in the cortex to about 1200 mOsmol L⁻¹ in the inner medulla.