ANSWERS

Which switch?
Big hint:   Light bulbs become hot after they're turned on.

Solution:  Turn on two of the switches for a couple minutes.  Then turn off one of the "on" switches.   When you enter the room, if the lamp is on, then the remaining "on" switch controls the lamp.  If the lamp is off, then feel the light bulb.  If the bulb is warm, then the switch that you turned on, then off, controls the lamp.  If the bulb is cold, then the third switch that was left off controls the lamp.

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