The correct option is A Osmoregulation
The kidneys are the excretory organ and essential for regulating the volume and composition of bodily fluids such as sodium and potassium concentrations and the pH of bodily fluids. Water and sodium regulation are integrated by the kidney to defend the body against all possible disturbances in the volume and osmolarity of bodily fluids are the osmoregulation. Thus, the correct answer is option A.