Which One of the Following Statements Concerning Electron Energy Bands

Which one of the following statements concerning electron energy bands in solids is true?

A) the bands occur as a direct consequence of the Fermi-Dirac distribution function
B) electrical conduction arises from the motion of electrons in completely filled bands
C) within a given band, all electron energy levels are equal to each other
D) an insulator has a large energy separation between the highest filled band and the lowest empty band
E) only insulators have energy bands