JS三级联动菜单，页面刷新后如何保持之前选择的项目？

<%@ Page Language="C#" AutoEventWireup="true" EnableEventValidation="false" CodeFile="Default6.aspx.cs" Inherits="Default6" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<!--更新日期2010-6-7-->
<html xmlns="http://www.w3.org/1999/xhtml" > 
<head id="Head1" runat="server"> 
    <title>AjaxTest </title> 
    
</head> 
<body> 
    <form id="form1" runat="server"> 
<td width=130px>始发地<select id="s1" name = "nm1" runat = server style="width:178px;" onchange = "getAddrs()"></select>
                                    <select id="s2" runat = server name = "nm2" style="width:178px;" onchange = "getAddrs()"></select>
                                    <select id="s3" runat = server name = "nm3" style="width:178px;" onchange = "getAddrs()"></select></td>
                    <td width=130px align=right>目的地</td><br />
                    <td width=130px><select id="sn1" name = "nm4" runat = server style="width:178px;" onchange = "getAddrs()"></select>
                                    <select id="sn2" name = "nm5" runat = server style="width:178px;" onchange = "getAddrs()"></select>
                                    <select id="sn3" name = "nm6" runat = server style="width:178px;" onchange = "getAddrs()"></select></td>    </form> 
</body> 
<script language="javascript" type="text/javascript">
    
  function LianDong(arr, sel)
    {
        this.GetCnNameByValue = function(val)
        {
            for ( var j = 0; j < arr.length; j++)
            {
                if (arr[j][0] == val)
                {
                    return arr[j][2];
                }
            }
            return "";
        }        this.GetValueByCnName = function(val)
        {
            for ( var j = 0; j < arr.length; j++)
            {
                if (arr[j][2] == val)
                {
                    return arr[j][0];
                }
            }
            return "";
        }        var me = this;
        this.$ = function(o)
        {
            return document.getElementById(o);
        }        this.sub = function (i, pid)
        {
            for (var j=i+1; j<sel.length; j++)
            {
               me.$(sel[j]).length = 0;
               me.$(sel[j]).options[0] = new Option("请选择省,直辖市", "");
               if(j=0)
               {
                    me.$(sel[j]).options[0] = new Option("请选择省,直辖市", "");
               }
               if(j=1)
               {
                    me.$(sel[j]).options[0] = new Option("市,直辖市", "");
               }
               if(j=2)
               {
                    me.$(sel[j]).options[0] = new Option("县", "");
               }
               
            }
            for ( var j = 0; j < arr.length; j++)
            {
                if (arr[j][1] == pid)
                {
                    me.$(sel[i+1]).options[me.$(sel[i+1]).length] = new Option(arr[j][2], arr[j][0]);
                }
            }
        }        this.init = function()
        {
            me.sub(-1,"root");
        for (var i=0; i<sel.length-1; i++)
        {
            me.$(sel[i]).onchange = function()
            {
                var i;
                for (i=0; me.$(sel[i])!=this; i++);
                me.sub(i, me.$(sel[i]).value);
            }
        }
    }
    this.SetValue = function()
    {
        for (var i=0; i<arguments.length-1; i++)
        {
           me.$(sel[i]).value = arguments[i];
           me.sub(i, me.$(sel[i]).value);
        }
        me.$(sel[arguments.length-1]).value = arguments[arguments.length-1];
    }
    this.init();
    }
    
    
    var sfcode = "3559,3478,........";
    var psfcode = "root,root,.......";
    var sfmingzi = "云南,浙江,新疆,西藏,重庆,天津.............";
    //此处代码太多，发不上来，已省略，，就是各个省市县的名称和代码。    var array=new Array();
    var sfcodearr = sfcode.split(",");
    var psfcodearr = psfcode.split(",");
    var sfmingziarr = sfmingzi.split(",");
for(var bvn=0;bvn<sfcodearr.length;bvn++)
    {
        array[bvn] = new Array(sfcodearr[bvn],psfcodearr[bvn],sfmingziarr[bvn]);
    }
    //初始化三个控件名字
    if(document.getElementById("s1")!=null && document.getElementById("s2")!=null && document.getElementById("s3")!=null)
    {
        var selectArr = new Array("s1","s2","s3");
        var liandong=new LianDong(array, selectArr);
    }    //初始化三个控件名字
    if(document.getElementById("sn1")!=null && document.getElementById("sn2")!=null && document.getElementById("sn3")!=null)
    {
        var selectArr = new Array("sn1","sn2","sn3");
        var liandong=new LianDong(array, selectArr);
    }
    </script> 
</html>
以上是代码比如我选择了  陕西省 西安市 市辖区如何在点击查询或者提交按钮页面刷新后，选择项还保持在  陕西省 西安市 市辖区