Which of the following reduction reactions are actually employed in commercial extraction of metals?
A. `Fe_(2)O_(3) + 2Al rarr Al_(2)O_(3)+Fe`
B. `Cr_(2)O_(3)+ 2Al rarr Al_(2)O_(3)+2Cr`
C. `2Na[Au(CN)_(2)]rarr Zn rarr Na[Zn(CN)_(4)]+2Au`
D. `Cu_(2)S + 2CuO rarr 6Cu + SO_(2)`