A bulb in a staircase has two switches, one switch being at the ground floor and the other one at the first floor. The bulb can be turned $ON$ and also can be turned $OFF$ by any one of the switches irrespective of the state of the other switch. The logic of switching of the bulb resembles
- an $AND$ gate
- an $OR$ gate
- an $XOR$ gate
- a $NAND$ gate
