Which of the following is true of semiconductors?

A. Exposing a crystal of a semiconductor to heat or light starts displacing valence electrons, which then move throughout the crystal.

B. A material is classified as a semiconductor if its resistance to the flow of electric current is too low to permit it to be called a conductor.

C. Neither free electrons nor holes are considered charge carriers in a semiconductor.

D. Gold and silver are important semiconductors

A. Exposing a crystal of a semiconductor to heat or light starts displacing valence electrons, which then move throughout the crystal.

Explanation:

A semiconductor has several properties, the main two are:

1. Under no special treatment and polarization conditions, there can't be current flow through it due to the high resistance.

2. The semiconductor material can have special change in its structure (excess of electron or holes), to be conductive under certain polarization situations.

B. A material is classified as a semiconductor if its resistance to the flow of electric current is too low to permit it to be called a conductor.

Explanation:

A material is classified as a semiconductor if its resistance to the flow of electric current is too low to permit it to be called a conductor is true of semiconductors.