What part of the swiss army knife can be used to pick locks?
D. Here is why the others are wrong. A- they don't prevent lightning, they attract it, so as not to damage other parts of the building. B- They are extremely conductive, to attract lightning to them C- they must be grounded to have a complete circuit for the electricity to travel through.
If you have a fan, turn it on and open a window to allow the residual smoke to leave. Once the smoke detector activates, the smoke must be very nearly entirely gone to re-set the unit. There is probably enough particles remaining in the air that you can't see or smell to keep re-activating the alarm. They will rise upward from the carpet, walls and everything.
