how to make a button to be clickable only ONCE.

I Have three answer choices for a question. (codes below)
if 1 button has been clicked, the other 2 buttons will be disabled.
But .. apparently, the same button can be clicked more than once. How do i do to stop that ? and only allow 1 click.

//CHOICE A
function ona1Click(evt:MouseEvent):void {

Q1a = new Loader();

bb1.removeEventListener(MouseEvent.CLICK, onb1Click);
cc1.removeEventListener(MouseEvent.CLICK, onc1Click);

var myQ1a:URLRequest=new URLRequest("wrong.png");
Q1a.load(myQ1a);
addChild(Q1a);

Q1a.x=320;
Q1a.y=180;
}

//CHOICE B
function onb1Click(evt:MouseEvent):void {

Q1b = new Loader();

aa1.removeEventListener(MouseEvent.CLICK, ona1Click);
cc1.removeEventListener(MouseEvent.CLICK, onc1Click);

var myQ1b:URLRequest=new URLRequest("tick.png");

correctAnswers++;

Q1b.load(myQ1b);
addChild(Q1b);

Q1b.x=320;
Q1b.y=260;
}

//CHOICE C
function onc1Click(evt:MouseEvent):void {

Q1c = new Loader();

aa1.removeEventListener(MouseEvent.CLICK, ona1Click);
bb1.removeEventListener(MouseEvent.CLICK, onb1Click);

var myQ1c:URLRequest=new URLRequest("wrong.png");
Q1c.load(myQ1c);
addChild(Q1c);

Q1c.x=320;
Q1c.y=340;
}

//NEXT --> AND REMOVE IMAGE
function onNext1Click(evt:MouseEvent):void {

if(Q1a)
removeChild(Q1a);

if (Q1b)
removeChild(Q1b);

if(Q1c)
removeChild(Q1c);

gotoAndPlay(4);

}

There are a few ways you could go about fixing this. This thread may help:
http://board.flashkit.com/board/show...a-single-click

Why not just removeListener() to the button clicked? An alternative is button.mouseEnabled = false - if you re-use the same buttons then just, change to true on reset.

I would create a function to Disable all buttons then call that function from your clicked function.

function disableButtons():void{
aa1.removeEventListener(MouseEvent.CLICK, ona1Click);
bb1.removeEventListener(MouseEvent.CLICK, onb1Click);
cc1.removeEventListener(MouseEvent.CLICK, onc1Click);
//or as steven FN said, you can use the .mouseEnabled method
}

funtion onb1Click(e:MouseEvent):void{
//all of your other code
disableButtons();
}