When the sample of copper with the zinc impurity is to be purified by electrolysis, the appropriate electrodes are
A. `{:("Cathode",,"Anode"),("Pure zinc",,"Pure copper"):}`
B. `{:("Cathode",,"Anode"),("Impure sample",,"Pure copper"):}`
C. `{:("Cathode",,"Anode"),("Impure zinc",,"Impure sample"):}`
D. `{:("Cathode",,"Anode"),("Pure copper",,"Impure sample"):}`