A xerographic copier uses a special photoconductor surface that allows light from an original document to control the placement of black powder on white paper. The photoconductor only conducts electricity when it's exposed to light because, in the dark:_________.

A) the photoconductor contains only negatively charged particles.

B) the photoconductor contains only positively charged particles.

C) electrons in the photoconductor completely fill its valence levels and can't shift from one level to another in order to transport charge through the material.

D) the photoconductor doesn't contain any electrically charged particles.