JS+XML 实现 省份和城市之间的联动

用JS来操作一个XML文档来实现一个简单的表单联动
这里是：xml文件
这里是：JS文件
aspx页面：
 <table cellspacing="0" cellpadding="0" width="100%" border="0">
            <tr>
                <td height="25" width="30%" align="right">
                    UName ：
                </td>
                <td height="25" width="*" align="left">
                    <asp:TextBox ID="txtUName" runat="server" Width="200px"></asp:TextBox>
                </td>
            </tr>         
            <tr>
                <td height="25" width="30%" align="right">
                    UCountry ：
                </td>
                <td height="25" width="*" align="left">
                    <asp:TextBox ID="txtUCountry" runat="server" Width="200px"></asp:TextBox>
                </td>
            </tr>
            <tr>
                <td height="25" width="30%" align="right">
                    UProvince ：
                </td>
                <td height="25" width="*" align="left">
                    <asp:DropDownList ID="ddlUProvince" runat="server"   onchange="ResetCity(this,'ddlUCity');">                 
                    </asp:DropDownList>
                </td>
            </tr>
            <tr>
                <td height="25" width="30%" align="right">
                    UCity ：
                </td>
                <td height="25" width="*" align="left">
                    <asp:DropDownList ID="ddlUCity" runat="server">
                    </asp:DropDownList>
                </td>
            </tr>
                     
            <tr>
                <td height="25" colspan="2">
                    <div align="center">
                        <asp:Button ID="btnAdd" runat="server" Text="注册" OnClick="btnAdd_Click"></asp:Button>
                    </div>
                </td>
            </tr>
        </table>
  <script>       

InitProvince('ddlUProvince');

 ResetCity(document.getElementById("ddlUProvince"), "ddlUCity");

</script>

aspx.cs：
string province=Request["ddlUProvince"];
string city=Request["ddlUCity"];