Which of the following reactions occurs at the cathode during the discharging of a lead accumulator?

• A
  $PbSO_{4(s)} + 2 e^{-} \longrightarrow Pb_{(s)} + SO_{4(aq)}^{2-}$
• B
  $Pb_{(s)} + SO_{4(aq)}^{2-} \longrightarrow PbSO_{4(s)} + 2 e^{-}$
• C
  $PbO_{2(s)} + 4 H_{(aq)}^{+} + SO_{4(aq)}^{2-} + 2 e^{-} \longrightarrow PbSO_{4(s)} + 2 H_2 O_{(l)}$
• D
  $PbSO_{4(s)} + 2 H_2 O_{(l)} \longrightarrow PbO_{2(s)} + 4 H_{(aq)}^{+} + SO_{4(aq)}^{2-} + 2 e^{-}$