What Mechanisms Are Responsible for Producing Concentrated Urine

Multiple Choice

What mechanisms are responsible for producing concentrated urine?

A) The juxtamedullary nephrons become active.
B) The counter-current mechanism pulls out much water.
C) Vasopressin causes facultative water reabsorption in distal tubule.
D) All of these.
E) The counter-current mechanism pulls out much water, and vasopressin causes facultative water reabsorption in distal tubule.