Ajax实现三级联动下拉框

jsp的代码：
<%
@ page contentType 
=
 
"
text/html; charset=GBK
"
  
import
=
"
java.util.*,com.wehave.hyerp.procurement.domain.Cgsqd
"
%>
<%
@ taglib uri
=
"
struts-html
"
 prefix
=
"
html
"
 
%>
<%
@ taglib uri
=
"
struts-logic
"
 prefix
=
"
logic
"
 
%>
<%
@ taglib uri
=
"
struts-bean
"
 prefix
=
"
bean
"
 
%>
<
html
>
    
<
head
>
        
<
title
>
 
</
title
>
        
<
link rel 
=
 
"
stylesheet
"
 type 
=
 
"
text/css
"
 href 
=
 
"
../css/olstyle.css
"
>
    
        
<
SCRIPT type
=
"
text/javascript
"
>
        var req;
        window.onload
=
function()
{
        }
        
        function Change_Select()
        
{
            var zhi
=
document.getElementById(
'
m_gykfwzlbb_lbbm
'
).value;
            var url
=
"
sqdSelect.go?method=getSkill&id=
"
+
zhi;
            
if
(zhi
==
"
0
"
)
{
                al