Question about my Drag and Drop script

I have a drag and drop interactivity and I have this script (below). What I want to add in but not sure how, is that if the user drags the wrong object to the main box it will make that object disappear. As well if the user drags over the correct object to the box the other objects disappear. Code is below:

square_mc.addEventListener(MouseEvent.MOUSE_DOWN, pickUp);
square_mc.addEventListener(MouseEvent.MOUSE_UP, dropIt);
triangle_mc.addEventListener(MouseEvent.MOUSE_DOWN, pickUp);
triangle_mc.addEventListener(MouseEvent.MOUSE_UP, dropIt);
pentagon_mc.addEventListener(MouseEvent.MOUSE_DOWN, pickUp);
pentagon_mc.addEventListener(MouseEvent.MOUSE_UP, dropIt);
function pickUp(event:MouseEvent):void {
event.target.startDrag(true);
reply_txt.text = “”;
}
function dropIt(event:MouseEvent):void {
event.target.stopDrag();
var myTargetName:String = “target” + event.target.name;
var myTargetDisplayObject = getChildByName(myTargetName);
if (event.target.dropTarget != null && event.target.dropTarget.parent == myTarget){
reply_txt.text = “Good Job! Click here the NEXT button to continue”;
event.target.removeEventListener(MouseEvent.MOUSE_DOWN, pickUp);
event.target.removeEventListener(MouseEvent.MOUSE_UP, dropIt);
event.target.buttonMode = false;
} else {
reply_txt.text = “Try Again!”;
}
}
square_mc.buttonMode = true;