List of questions in Array are not properly presented - actionscript-3

Question

I used Array to present my set of questions in my project. Below are the coding that I used. I've tried the coding for 3 questions and it worked well. For my real project, I need to put 20 questions and when everything done, I run the project, it didnt work well. I hit next, start on Q3, it will give Q5, then Q8 and jump to Q17. Why does it happen?
stop();
var finalString:String = '';
//var finalString2:String = '';
var _list:Array = ["Q1", "Q2", "Q3,"Q4,"Q5 ","Q6","Q7","Q8 ","Q9","Q10","Q11","Q12", "Q13","Q14", "Q15", "Q16","Q17", "Q18", "Q19", "Q20"];
var _marks:Array = [];
var i:int;
var myscore = 0;
////////////////////////////////////////////
buttonA.buttonMode = true;
buttonB.buttonMode = true;
buttonC.buttonMode = true;
buttonD.buttonMode = true;
skip_btn.buttonMode = true;
score_txt.text = myscore;
question_txt.text = _list[0];
buttonA.label_txt.text = "A. ";
buttonB.label_txt.text = "B. ";
buttonC.label_txt.text = "C. ";
buttonD.label_txt.text = "D. ";
skip_btn.label_txt.text = "SKIP";
buttonA.label_txt.mouseEnabled = buttonB.label_txt.mouseEnabled = buttonC.label_txt.mouseEnabled = buttonD.label_txt.mouseEnabled = skip_btn.label_txt.mouseEnabled = false;
buttonA.addEventListener(MouseEvent.CLICK, q1);
buttonB.addEventListener(MouseEvent.CLICK, q1);
buttonC.addEventListener(MouseEvent.CLICK, q1);
buttonD.addEventListener(MouseEvent.CLICK, q1);
skip_btn.addEventListener(MouseEvent.CLICK, q1);
function q1(event:MouseEvent):void
{
if(event.currentTarget == buttonA)
{
_marks.push("Your answer: ");
}
else if(event.currentTarget == buttonB)
{
_marks.push("Your answer:");
}
else if(event.currentTarget == buttonC)
{
_marks.push("Your answer:");
myscore+=5;
}
else if(event.currentTarget == buttonD)
{
_marks.push("Your answer:");
}
else if(event.currentTarget == skip_btn)
{
_marks.push("Skip");
}
buttonA.removeEventListener(MouseEvent.CLICK, q1);
buttonB.removeEventListener(MouseEvent.CLICK, q1);
buttonC.removeEventListener(MouseEvent.CLICK, q1);
buttonD.removeEventListener(MouseEvent.CLICK, q1);
skip_btn.removeEventListener(MouseEvent.CLICK, q1);
nextFrame();
}