flash怎么使用RadioButton制作选择题?

var right_index:int=3;
var selected_index:int=-1;
initSence();
function initSence():void
{
for(var i:int=0;i<4;i++)
{
this["l"+i].addEventListener(MouseEvent.CLICK,SelectEvent);
}
btn_submit.addEventListener(MouseEvent.CLICK,SubmitAnswer);
}
function SelectEvent(e:MouseEvent):void
{
var obj:Object=e.target;
selected_index=int(obj.name.slice(1));
}
function SubmitAnswer(e:MouseEvent):void
{
if(selected_index==-1)
{
txt.text="请选择答案后点击确定！";
}
else if(selected_index==right_index)
{
txt.text="选择正确！";
}
else
{
txt.text="选择错误！";
}
}