function checkBoxClick(form,correct,number,clicked)
{
   var rightlayer  = "right"+number;
   var wronglayer  = "wrong"+number;
   var replylayer  = "reply"+number;
   var useranswer  = "";
   var trueanswer  = "";
   var replynumber =  0;

   // create 'binary' string of users answers

   for(x=0;x<5;x++)
   {
      if(form.elements[x].checked == true)
      {
         useranswer = useranswer+"1";
      }
      else
      {
         useranswer = useranswer+"0";
      }
   }


   // create 'binary' string of correct answers

   for(x=0;x<5;x++)
   {
      y=x+1;

      ystring = y.toString();

      if (correct.indexOf(ystring,0) != -1)
      {
         trueanswer = trueanswer+"1";
      }
      else
      {
         trueanswer = trueanswer+"0";
      }
   }

   // select appropriate reply to display

   if(useranswer == trueanswer) // all correct and none incorrect
   {
      replynumber = 1;
   }
   else if(useranswer == "00000")  // none checked
   {
      replynumber = 4;
   }
   else
   {
      for(y=0;y<5;y++)
      {
         if(useranswer.charAt(y) == "1" && trueanswer.charAt(y) == "0")
         {
            replynumber = 3;
            break;
         }
         else
         {
            replynumber = 2;
         }
      }
   }

   replylayer = replylayer+replynumber;


   // ensure all reply layers are invisible

   for(x=1;x<=4;x++)
   {
      thislayer = "reply"+number+x; // number is group number
      
      if(document.layers)
      {
         document.layers[thislayer].className="respoff";
      }
      else if (document.all)
      {
         document.all[thislayer].className="respoff";
      }
      else
      {
         document.getElementById(thislayer).className="respoff";
      }
   }


   // make visible the appropriate reply layer

   if(document.layers)
   {
        document.layers[replylayer].className="respon";
   }
   else if (document.all)
   {
        document.all[replylayer].className="respon";
   }
   else
   {
        document.getElementById(replylayer).className="respon";
   }
}