In the electrolytic refining of a metal $M$,what would you take as the anode,the cathode,and the electrolyte?

• A
  Anode: Pure metal $M$,Cathode: Impure metal $M$,Electrolyte: Salt solution of metal $M$
• B
  Anode: Impure metal $M$,Cathode: Pure metal $M$,Electrolyte: Salt solution of metal $M$
• C
  Anode: Impure metal $M$,Cathode: Impure metal $M$,Electrolyte: Pure metal $M$
• D
  Anode: Pure metal $M$,Cathode: Pure metal $M$,Electrolyte: Impure metal $M$