[chamele0n]

так чтоли ?

private var question_id:int = 0;
 
function xmlLoaded(event:Event):void {
 myList = new XML(event.target.data);
 myList.ignoreWhite = true; 
 questionTxt.text = myList.excercise[question_id].question;           
 checkBtn.addEventListener(MouseEvent.CLICK, nextAnswer);
}
 
function nextAnswer(event:MouseEvent) : void {
 if(question_id == myList.excercise.length()) {
    trace('end test');
    return;
 }       
 if (answerTxt.text == myList.excercise[question_id].answer) {
    question_id++;
    questionTxt.text = myList.excercise[question_id].question;
 }
}