ช่วยหน่อยครับ เรื่อง listbox ซ้อนกัน 3 อัน ครับ

<?php
header("Content-type:text/html; charset=UTF-8");
header("Cache-Control: no-store, no-cache, must-revalidate");
header("Cache-Control: post-check=0, pre-check=0", false);
include('../serverdb/connect.php');
?>
<script src="../serverweb/js/jquery.min.js"></script>
<script type="text/javascript">
    $(function(){
        $("select#listApp").change(function(){
            var datalistOS = $.ajax({
                url: "r1.php",
                data:"app="+$(this).val(),
                async: false
            }).responseText;
            $("select#listOS").html(datalistOS);
        });
    });
    $(function(){
        $("select#listOS").change(function(){
            var datalistBanner = $.ajax({
                url: "r2.php",
                data:"os="+$(this).val(), //ต้องการส่ง param app ไปเช็ค
                async: false
            }).responseText;
            $("select#listBanner").html(datalistBanner);
        });
    });
</script>
<h2>Test</h2>
<form action="" method="post">
    <table width="100%">
        <?php
        $result = pg_query("SELECT * FROM atappadsbanner ORDER BY app_ads_name ASC");
        ?>
        <td align="right">APP</td>
        <td><select name="listApp" id="listApp">
                <option value="0">-- เลือก Application --</option>
                <?php while($rs= pg_fetch_array($result)){ ?>
                    <option value="<?php echo $rs['app_ads_name'];?>"><?php echo $rs['app_ads_name'];?></option>
                <?php } ?>
            </select></td>
        </tr>
        <tr>
            <td align="right">OS</td>
            <td><select name="listOS" id="listOS">
                    <option value="0">-- เลือก OS --</option>
                </select></td>
        </tr>
        <tr>
            <td align="right">BANNER</td>
            <td><select name="listBanner" id="listBanner">
                    <option value="0">-- เลือก Banner --</option>
                </select></td>
        </tr>
    </table>

<?php
header("Content-type: application/xhtml+xml; charset=utf-8");
header("Cache-Control: no-cache, must-revalidate"); // HTTP/1.1
include('../serverdb/connect.php');
//$province_id = $_GET['province_id'];
$app = $_GET['app'];
$result = pg_query("SELECT * FROM atappadsbanner WHERE app_ads_name = '$app'" );
if(isset($_GET['app']) && $_GET['app']!=""){
    ?>
    <option value="">เลือกรายการ</option>
    <?php while($rs= pg_fetch_array($result)){ ?>
        <option value="<?php echo $rs['app_ads_os'];?>"><?php echo $rs['app_ads_os'];?></option>
    <?php } ?>
<?php }else{ ?>
    <option value="">เลือกรายการ</option>
<?php } ?>

<?php
header("Content-type: application/xhtml+xml; charset=utf-8");
header("Cache-Control: no-cache, must-revalidate"); // HTTP/1.1
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT"); // Date in the past

include('../serverdb/connect.php');
$os = $_GET['os'];
//$sql= "SELECT * FROM tbl_district WHERE amphur_id = ".$amphur_id."  ORDER BY district_name ASC";
$result = pg_query("SELECT * FROM atappadsbannerlist t1
INNER JOIN atappbanner t2 ON t1.app_banner_id = t2.app_banner_id
WHERE t1.app_ads_os = '$os' AND t1.app_ads_name = 'ตัวแปร app จาก listApp'");
if(isset($_GET['os']) && $_GET['os']!=""){
    ?>
    <option value="">เลือกรายการ</option>
    <?php while($rs=pg_fetch_array($result)){ ?>
        <option value="<?php echo $rs['app_banner_id'];?>"><?php echo $rs['app_banner_name'];?></option>
    <?php } ?>
<?php }else{ ?>
    <option value="">เลือกรายการ</option>
<?php } ?>