ajax เลือกจังหวัด อำเภอ ตำบล ไม่ยอมส่งค่าkey ที่เรา select ใน chrome

<tr>
       <td align="right">จังหวัด  :</td>
       <td><font id="province"><select><option value="0">=========================</option></select></font></td>
</tr>
<tr>
       <td align="right">อำเภอ/เขต  :</td>
       <td><font id="amphur"><select><option value="0">=========================</option></select></font></td>
</tr>
<tr>
           <td align="right">ตำบล/แขวง  :</td>
           <td><font id="tumbon"><select><option value="0">=========================</option></select></font></td>
</tr>

function Inint_AJAX() {
   try { return new ActiveXObject("Msxml2.XMLHTTP");  } catch(e) {} //IE
   try { return new ActiveXObject("Microsoft.XMLHTTP"); } catch(e) {} //IE
   try { return new XMLHttpRequest();          } catch(e) {} //Native Javascript
   alert("XMLHttpRequest not supported");
   return null;
};

function dochange(src, val) {
     var req = Inint_AJAX();
     req.onreadystatechange = function () { 
          if (req.readyState==4) {
               if (req.status==200) {
                    document.getElementById(src).innerHTML=req.responseText; //รับค่ากลับมา
               } 
          }
     };
     req.open("GET", "province.php?data="+src+"&val="+val); //สร้าง connection
     req.setRequestHeader("Content-Type", "application/x-www-form-urlencoded;charset=utf-8"); // set Header
     req.send(null); //ส่งค่า
}

window.onLoad=dochange('province', -1);

header("content-type: text/html; charset=utf-8");
header ("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
header ("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
header ("Cache-Control: no-cache, must-revalidate");
header ("Pragma: no-cache");

include "connect.php";
conndb();
          
$data = $_GET['data'];
$val = $_GET['val'];


     if ($data=='province') { 
          echo "<select name='province' onChange=\"dochange('amphur', this.value)\">\n";
          echo "<option value='0'>==== กรุณาเลือกจังหวัด ====</option>\n";
          $result=mysql_db_query($dbname,"select * from province order by ProvinceName");
          while($row = mysql_fetch_array($result)){
               echo "<option value=\"$row[ProvinceID]\" >$row[ProvinceName]</option> \n" ;
          }
     } else if ($data=='amphur') {
          echo "<select name='amphur' onChange=\"dochange('tumbon', this.value)\">\n";
          echo "<option value='0'>========= กรุณาเลือกอำเภอ =========</option>\n";                             
          $result=mysql_db_query($dbname,"SELECT * FROM amphur WHERE ProvinceID = '$val' ORDER BY AmphurName");
          while($row = mysql_fetch_array($result)){
               echo "<option value=\"$row[AmphurID]\" >$row[AmphurName]</option> \n" ;
          }
     } else if ($data=='tumbon') {
          echo "<select name='tumbon'>\n";
          echo "<option value='0'>========= กรุณาเลือกตำบล =========</option>\n";
          $result=mysql_db_query($dbname,"SELECT * FROM tumbon WHERE AmphurID = '$val' ORDER BY TumbonName");
          while($row = mysql_fetch_array($result)){
               echo "<option value=\"$row[TumbonID]\" >$row[TumbonName]</option> \n" ;
          }
     }
     echo "</select>\n";

echo mysql_error();
closedb();

<tr>
       <td align="right">จังหวัด  :</td>
       <td><font id="province"><select><option value="0">=========================</option>
     
       // query ข้อมูลของจังหวัด ใส่เข้าไปในนี้ก่อน

</select></font></td>
</tr>