How to create button group like RadioButton group?

Hi. I was trying to create button group as in the radio button group function. I've changed few things to fit the condition as button.

But the errors I got are :

Scene 1, Layer 'Actions', Frame 2, Line 19    1119: Access of possibly undefined property selection through a reference with static type fl.controls:Button.

Scene 1, Layer 'Actions', Frame 2, Line 14    1119: Access of possibly undefined property group through a reference with static type flash.display:SimpleButton.

Anyone can help me? Thank you.

Here is my coding

//using the import directive to import the required class

//import fl.controls.RadioButtonGroup;

import flash.events.MouseEvent;

import flash.events.TimerEvent;

import flash.utils.Timer;

import fl.controls.Button;

import flashx.textLayout.events.ModelChange;

//starting out with a score of 0

var myscore = 0; score.text = myscore+"";

//creating a new instances for RadioButtonGroup Class

var mygroup1:Button = new Button("group1");

q1a.group = q1b.group = q1c.group = q1d.group = mygroup1;

next1.addEventListener(MouseEvent.CLICK, quizHandler1)

function quizHandler1 (event:MouseEvent):void

{

    if(mygroup1.selection == "q1c")

    {

        myscore+=2; nextFrame();

        //correct.visible = true;

    }

    else

    {

        nextFrame();

        //correct.visible = false;

    }

}

myTimer.start();*/

var endTime:int = getTimer();

endTime += 40*60*1000;  //adjust endTime to 15 minutes in the future.

var countdownTimer:Timer = new Timer(1000);

countdownTimer.addEventListener(TimerEvent.TIMER, updateTime);

countdownTimer.start();

function updateTime(e:TimerEvent):void

{

  var timeLeft:Number = endTime - getTimer();

  var seconds:Number = Math.floor(timeLeft / 1000);

  var minutes:Number = Math.floor(seconds / 60);

  seconds %= 60;

  minutes %= 60;

  var sec:String = seconds.toString();

  var min:String = minutes.toString();

  if (sec.length < 2) {

    sec = "0" + sec;

  }

  if (min.length < 2) {

    min = "0" + min;

  }

  var time:String = min + ":" + sec;

  timer.text = time;

}