Ans. (D). nephron.
Kidneys are bean-shaped organs of excretory system that make urine and help in elimination of wastes from the body. Nephrons can be defined as structural and functional units of kidneys, made up of renal tubes and renal capsules.
Process of filtration, re-absorption, and secretion take place in nephrons to filter blood, make urine and excrete waste products out from the body with urine.
Thus, the correct answer is option (D).
