According to the Band Theory, Why Is a Material Such

Multiple Choice

According to the band theory, why is a material such as diamond an insulator?

A) All of the electrons are in the conduction band.
B) All of the electrons are tied to nuclei.
C) Very few electrons can make the transition over the large energy gap between the valence band and the conduction band.
D) The bonds in diamond are too strong to allow atoms to move so no current flows.
E) There are no electrons in the valence band.