You are in a house. There are 3 light switches. Inside of a closed room (that you CAN NOT see) there is a light bulb that is turned on by one of the switches. If you can only go inside the room one time how can you tell
[Only registered and activated users can see links. Register now...][Only registered and activated users can see links. Register now...][Only registered and activated users can see links. Register now...] which switch turns on the light?