anchor.diff:  
           function disableDivs() {
               var L1 = $('L1');
  -            $(L1).style.display = "inline"
  -            var arrayOfSiblings = $('L1').siblings();
  -            for (var i = 0; i < arrayOfSiblings.length; i++){
  -                $(arrayOfSiblings[i]).style.display = "none";
  +            if (L1 != null) {
  +                $(L1).style.display = "inline"
  +                var arrayOfSiblings = $('L1').siblings();
  +                for (var i = 0; i < arrayOfSiblings.length; i++){
  +                    $(arrayOfSiblings[i]).style.display = "none";
  +                }
               }
   
               var R2 = $('R2');
  
positive.code:                         $(arrayOfSiblings[i]).style.display = "none";
                      }
                  }
                  $('nextTenStudies').hide()
              }
          }
  
  
negative.code:                 afterUpdateElement:updateActivity,
                  revertOnEsc:true
              });
                  }
          }
  
          function updateActivity(input, li) {
  