C.
If a power line were broken then power would not reach the light. Which is possible.
If a wire to the light or to the box in your house was broken your light would not receive power, therefore not turn on. Again possible.
If the power plant does not produce enough electricity, although unlikely, that would cause you to not be able to turn on your light. Unlikely but it would be true is it happened.
Finally C is not likely, your wires in your house are most likely made of copper but too many conductors in the wire, not only wouldn’t happen, but would most likely not interrupt your light working.
The question asks what is NOT a possible cause. C is the only not possible.
