In the electrolysis of aqueous solution of CuSO₄ using copper electrodes, the process taking place at the anode is:
A. SO²⁻₄ → SO₄ + 2e⁻
B. Cu → Cu⁺ + e⁻
C. 2OH⁻ → H₂O + 1/2 O₂ + 2e⁻
D. Cu → Cu²⁺ + e⁻