The correct statement variation of the conductivity of semiconductors like Ge and Si is given by

Options

A. Increases when it is doped wirh tetravalent impurity
B. Increases when it is doped with pentavalent or trivalent impurity
C. Increases when it is doped with pentavalent impurity and decreases when it is doped with trivalent impurity
D. Decreases when it is doped with pentavalent impurity and increases when it is doped with trivalent impurity.