Each nephron has two parts – the glomerulus and the renal tubule. Therefore statement I is incorrect. On an average, 1100-1200 ml of blood is filtered by the kidneys per minute which constitute roughly 1/5th of the blood pumped out by each ventricle of the heart in a minute. Therefore statement II is incorrect. JGA is a special sensitive region formed by cellular modifications in the distal convoluted tubule and the afferent arteriole at the location of their contact. Therefore statement III is incorrect. Human kidneys can produce urine nearly four times concentrated than the initial filtrate formed. Presence of interstitial gradient helps in an easy passage of water from the collecting tubule thereby concentrating the filtrate (urine). Hence the correct option is D.