ถ้าเราจะทำให้ dropdown ไม่ให้เลือกซ้ำสามารถทำได้ไหมคะ ทำยังไง

 <script src="http://code.jquery.com/jquery-1.8.3.js "></script>
  <meta http-equiv="Content-Type" content="text/html; charset=utf8" />
  <script type="text/javascript">
  $(document).ready(function(){
	$("select.nodup").change(function(){
		var curSelection = $(this).attr("for")-1,
			curOption = $("option:selected",this).val();
		$("select.nodup").each(function(index,value){
			if(curSelection != index){
				$("option[value='"+curOption+"']",this)
				.attr("disabled","disabled");
			}
		});
	});
  });
  </script>

  <select class='nodup' for='1'>
    <option>please select</option>
    <option value='AAAAA'>AAAAA</option>
    <option value='BBBBB'>BBBBB</option>
    <option value='CCCCC'>CCCCC</option>
    <option value='DDDDD'>DDDDD</option>
</select>  <br /> 
<select class='nodup' for='2'>
    <option>please select</option>
    <option value='AAAAA'>AAAAA</option>
    <option value='BBBBB'>BBBBB</option>
    <option value='CCCCC'>CCCCC</option>
    <option value='DDDDD'>DDDDD</option>
</select>  <br /> 
<select class='nodup' for='3'>
    <option>please select</option>
    <option value='AAAAA'>AAAAA</option>
    <option value='BBBBB'>BBBBB</option>
    <option value='CCCCC'>CCCCC</option>
    <option value='DDDDD'>DDDDD</option>
</select>  <br />