In an n-type semiconductor, which of the following is true of impurity atoms? Select one: O a. They accept electrons from the filled valence band into empty energy levels just below the valence band. O b. They donate electrons to the filled valence band from the donor levels just above the valence band. O C They donate electrons to the conduction band from filled donor levels just below the conduction band. O d. They accept electrons from the filled valence band into empty energy levels just above the valence band.