Correct Option: AExplanation:Excretion is an essential process in all forms of life. It is a process in which metabolic waste is eliminated from the body of an organism. Accumulation of these wastes beyond a level inside the body is harmful to the body of an organism.In mammals, urine is expelled with the help of the excretory system. In unicellular organisms, waste products are discharged directly through the surface of the cell.In green plants, excretory gases like carbon dioxide and oxygen exit the plant body through stomata, root cell walls, etc. They also eliminate waste materials in the form of resin, saps, latex, etc.Hence, excretion is the removal of harmful metabolic wastes from the body.