Jquery自动完成功能无法在IE8中运行

Question

http://jqueryui.com/autocomplete/

function getclassno(cat){   
    $.ajax({ 
        type: "POST", 
        url:"reg/data/data.php", 
        data:{
            catogery:cat  
        },
        success: function(data){     
            $.each(data, function (i, elem) {        
                $('#classno').append( new Option(elem.id) );            
            });              
        }
    );

    $result = mysql_query("SELECT SUBJECTCODE  FROM subjectmaster WHERE CATCODE = '$cat'");  
    header('Content-type: application/json');
    $return_arr = array(); 

    while($row = mysql_fetch_array($result))
    {
        $row_array['id']=$row[0];     
        array_push($return_arr,$row_array);    
    }

    echo json_encode($return_arr);         
}

我使用上面的代码用data.it在Firefox和Chrome中填充自动填充，但在IE8中不运行