ขอความช่วยเหลือเรื่อง clone หน่อยครับเพราะว่าเวลาผม cloneแล้วมันเอาค่า value ไปด้วยครับ

<form id="form1" name="form1" method="post" action="">
<table id="myTbl" width="650" border="1" cellspacing="2" cellpadding="0">
  <tr id="firstTr">
    <td>
    <?    
     echo "<form name=sel>\n";
     echo "วิชา : <font id=course><select>\n";
     echo "<option value='0'>============</option> \n" ;
     echo "</select></font>\n";
     
     echo "เรื่อง : <font id=chapter><select>\n";
     echo "<option value='0'>=== none ===</option> \n" ;
     echo "</select></font>\n";

     echo "<img id='preview[]'>";
?>
</td>
    </tr>
</table>
<br />
<table width="500" border="0" cellspacing="0" cellpadding="0">
  <tr>
    <td>
    <button id="addRow" type="button">+</button>  
    &nbsp;
    <button id="removeRow" type="button">-</button>
  &nbsp;
    &nbsp;
    &nbsp;
    <button id="Submit" type="submit">Submit</button>    
    </td>
  </tr>
</table>
</form>

<script src="http://code.jquery.com/jquery-1.4.1.js"></script>
<script type="text/javascript">
$(function(){
  $("#addRow").click(function(){
    $("#myTbl").append($("#firstTr").clone());
  });
  $("#removeRow").click(function(){
    if($("#myTbl tr").size()>1){
      $("#myTbl tr:last").remove();
    }else{
      alert("ต้องมีรายการข้อมูลอย่างน้อย 1 รายการ");
    }
  });     
});
</script>

<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; //retuen value
      }
 }
};
req.open("GET", "testdrop.php?data="+src+"&val="+val); //make connection
req.setRequestHeader("Content-Type", "application/x-www-form-urlencoded;charset=iso-8859-1"); // set Header
req.send(null); //send value
}

window.onLoad=dochange('course', -1);         // value in first dropdown
</script>

<?
session_start();

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

//set database
include ('db.php');

if ($data=='course') {  // first dropdown
  echo "<select name='course[]' onChange=\"dochange('chapter', this.value)\">\n";
  echo "<option value='0'>==== choose state ====</option>\n";
  $result=mysql_db_query("WEBAN","SELECT * FROM course order by course_id ASC");
  while(list($id, $name)=mysql_fetch_array($result)){
       echo "<option value=\"$id\" >$name</option> \n" ;
  }
} else if ($data=='chapter') { // second dropdown
  echo "<select name='chapter[]' onchange=\"document.getElementById('preview[]').src = this.value\">\n";
  echo "<option value='0'>====choose chapter ====</option>\n";                   
  $result=mysql_db_query("WEBAN","SELECT chapter_path , chapter_name FROM Chapter WHERE course_id_ref = '$val' ORDER BY chapter_id ASC ");
  while(list($id, $name)=mysql_fetch_array($result)){
  ?>
       <option value="http://www.caiproject.com/<?=$id;?>pic.png" ><?=$name;?></option>


  <?
  }
}
echo "</select>";
session_destroy();
?>