Make UI yes or no toggle box

Questions & Answers
1

In my scene there is two boxes. A yes and a no. I want it so they are always opposites of each other. So when i toggle one, the other one gets toggled off. So there is alway one which is off and one on.
How do i achieve this?¨
I use js.

2

var box1 : boolean =true;
var box2 : boolean = false;

    function Update () {
    		if (Input.GetKeyDown ("space") && box1=true;){
    		//Replace with you're mouse click on UI box.
                    box1 = false;
                    box2 = true;
    }

    		if (Input.GetKeyDown ("space") && box1=false;){
    		//Replace with you're mouse click on UI box.
                    box1 = true;
                    box2 = false;
    }
    	}

Hope thats some help, not sure if you were looking to get the UI part working instead.