I think Rover might have pressed "Submit" too soon!
You are right that A and B are correct, although "One" could be changed to "You" and it would still be correct. We refer to electrics as being "live", not "alive".
Be careful, there's a live electric cable there.
I found out it was live when I stuck my finger on it and ended up in hospital.
"Electrical" is being used as an adjective to describe the type of fire, so the adjective "electrical" is correct.
I have an issue with the sentence as a whole. Quite simply, "one should never throw water on an electrical fire". If I found an electric heater or fan on fire, I wouldn't waste time finding out if it was plugged in or not, I would assume that it was "live" and I would not put water anywhere near it.
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