ช่วยผมหน่อยครับ T^T ต้องการทำดรอปดาวต่อๆกัน เหมือนเวลาเลือกจังหวัด อำเภอ ตำบล ครับ

<script language=Javascript>
        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", "localtion_cla.php?data2="+src+"&val2="+val); //สร้าง connection
             req.setRequestHeader("Content-Type", "application/x-www-form-urlencoded;charset=utf-8"); // set Header
             req.send(null); //ส่งค่า
        }

        window.onLoad=dochange('policestation', -1);     
        </script>

<?php 
          $policestation="SELECT * from policestation ";  
          $policestations=mysql_query($policestation);
         ?>
<div class="row">
        <label for="inputNo" class="col-sm-2 control-label" align="right">สถานีตำรวจภูธร : </label>
        <div class="col-xs-2" name="policestation">
        <span id="policestation">
                    <select class="col-sm-3 form-control">
                        <option value="0">- เลือกสภ. -</option>
                    </select>
                </span>
          </div>

        </div> <!--div class="row"-->
        <br>
        <div class="row">
        <label for="inputNo" class="col-sm-2 control-label" align="right">1. รับแจ้งจาก : </label>
        <div class="col-sm-2"  name="clamant">
          <span id="clamant">
                    <select class="col-sm-3 form-control">
                        <option value='0'>- ผู้รับแจ้ง -</option>
                    </select>
                </span>
          </div>
        </div> <!--div class="row"-->

<?php
    header("content-type: text/html; charset=utf-8");
    header ("Expires: Wed, 21 Aug 2013 13:13:13 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 "config.php";
    conndb();

    $data = $_GET['data2'];
    $val = $_GET['val2'];

  
         if ($data=='policestation') { 
              echo "<select class='col-sm-3 form-control' name='policestation' onChange=\"dochange('clamant', this.value)\">";
              echo "<option value='0'>- สถานีตำรวจ -</option>\n";
              $result=mysql_query("select * from policestation order by policestation_name");
              while($row = mysql_fetch_array($result)){
                   echo "<option value='$row[policestation_id]' >$row[policestation_name]</option>" ;
              }
         } else if ($data=='clamant') {
              echo "<select class='col-sm-3 form-control' name='clamant' onChange=\"dochange('clamantname', this.value)\">";
              echo "<option value='0'>- รหัสเจ้าหน้าที่ -</option>\n";                             
              $result=mysql_query("SELECT * FROM clamant WHERE policestation_id= '$val' order by clamant_id");
              while($row = mysql_fetch_array($result)){
                   echo "<option value=\"$row[clamant_id]\" >$row[clamant_id]</option> " ;
              }
         } 
         }
         echo "</select>\n";
echo mysql_error();
        closedb();
?>