The correct answer is regulation of lymphocyte production. Â
Kidneys have a function in:
·    regulation of blood pressure (through the regulation of the volume of blood in the body);
·    regulation of acid-base balance (by excreting H+ into the urine and reabsorbing HCO3- from the urine);
·    removal of wastes from the blood (through the urine);
·    regulation of erythrocyte production (producing erythropoietin hormone).
