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Riddle: 3 Lightbulb Switches

There are 3 switches outside of a room, all in the 'off' setting. One of them controls a lightbulb inside the room, the other two do nothing.

You cannot see into the room, and once you open the door to the room, you cannot flip any of the switches any more.

Before going into the room, how would you flip the switches in order to be able to tell which switch controls the light bulb?

You don't need to go into the room right away.

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