The correct option is C Quick short circuit for elimination of nitrogenous wastes
The hind limbs of frog are the most active organs. The blood coming form the hind limbs contain a considerable large amount of metabolic wastes. Through the renal portal system this blood comes into the kidneys. The renal portal system forms a network of blood capillaries around the uriniferous tubules of the kidney.Thus the cells of the uriniferous tubules are able to absorb the metabolic wastes from these capillaries and render the blood free from harmful wastes.
So, the correct answer is 'Quick short circuit for elimination of nitrogenous wastes'.