A parallel plate condenser of capacity C is connected to a battery and is charged to a potential V. Another condenser of capacity 2 C is connected to another battery and is charged to a potential 2 V. The charging batteries are removed and now the condensers are connected in parallel in such a way that the positive plate of one is connected to negative plate of other. The final energy of this system is

• A

  zero

• B

  $3{\mathrm{CV}}^2/2$

• C

  $5{\mathrm{CV}}^2/2$

• D

  $9{\mathrm{CV}}^2/2$