Equal but opposite charges Q are placed on the square plates of an airfilled parallel-plate capacitor. The plates are then pulled apart to twice their original separation, which is small compared to the dimensions of the plates.

Which of the following statements about this capacitor are true? (There may be more than one correct choice)

A) The energy stored in the capacitor has doubled.
B) The energy density in the capacitor has increased.
C) The electric field between the plates has increased.
D) The potential difference across the plates has doubled.
E) The capactiance has doubled.

Please explain why you chose that answer.