Described here is a simple electronic circuit which can be used in any test or quiz competition. Features of this circuit are:Whenever a switch is pressed, the [[wysiwyg_imageupload::]]circuit locks the remaining three entries. It has a master reset switch which allows users to press the switch next time once they have pressed. It can be powered from variable power supply ranging from 5V to 15V.Initially it may possible all or may two LED will be glowing for that you have to first clear the flip flop by pressing reset switch. Under this condition Q output of IC2 and IC1 become low.Continue reading to find out assembling and working of the circuit with video.