Which of the following statements best describes the role of the juxtamedullary nephrons?

• A. Juxtamedullary nephrons filter large volumes of blood to increase urine volume.
• B. Juxtamedullary nephrons play a role in forming concentrated urine.
• C. Juxtamedullary nephrons play a key role in regulating blood pressure.
• D. Juxtamedullary nephrons control $K^+$ and $Ca^2$$^+$ levels.