Kidneys seem to have evolved in primitive freshwater vertebrates to help them expel the excess water that continuously entered the body by osmosis. Later, kidneys also acquired the function of removing the waste materials from body.
The kidneys in vertebrates are bean-shaped organs that remove excess organic molecules from the blood, and waste products of metabolism. In protozoans, the contractile vacuole does the function of the kidneys of vertebrates and expels the excess water from the system.
Therefore, the correct answer is option c.