现在有这样一个程序：
选中“一级菜单A--一级菜单A_1--一级菜单A_0”，我想在<script>中添加一个function，使我获得选中的元素，格式就是：一级菜单A--一级菜单A_1--一级菜单A_0。请问需要怎样修改程序呢？附上部分程序内容。
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>三级折叠菜单</title>
<script language="JavaScript">
<!--//
function ShowMenu(obj,n){
var Nav = obj.parentNode;
if(!Nav.id){
var BName = Nav.getElementsByTagName("ul");
var HName = Nav.getElementsByTagName("h2");
var t = 2;
}else{
var BName = document.getElementById(Nav.id).getElementsByTagName("span");
var HName = document.getElementById(Nav.id).getElementsByTagName("h1");
var t = 1;
}
for(var i=0; i<HName.length;i++){
HName[i].innerHTML = HName[i].innerHTML.replace("-","+");
HName[i].className = "";
obj.className = "h" + t;
}
for(var i=0; i<BName.length; i++){if(i!=n){BName[i].className = "no";}}
if(BName[n].className == "no"){
BName[n].className = "";
obj.innerHTML = obj.innerHTML.replace("+","-");
}else{
BName[n].className = "no";
obj.className = "";
obj.innerHTML = obj.innerHTML.replace("-","+");
}
}
//-->
</script>
</head>
<body>
<div id="menu">
<h1 onClick="javascript:ShowMenu(this,0)"><a href="javascript:void(0)">+ 一级菜单A</a></a></h1>
<span class="no">
<h2 onClick="javascript:ShowMenu(this,0)"><a href="javascript:void(0)">+ 一级菜单A_1</a></a></h2>
<ul class="no">
<a href="javascript:void(0)">一级菜单A_0</a>
<a href="javascript:void(0)">一级菜单A_1</a>
<a href="javascript:void(0)">一级菜单A_2</a>
<a href="javascript:void(0)">一级菜单A_3</a>
<a href="javascript:void(0)">一级菜单A_4</a>
<a href="javascript:void(0)">一级菜单A_5</a>
<a href="javascript:void(0)">一级菜单A_6</a>
<a href="javascript:void(0)">一级菜单A_7</a>
<a href="javascript:void(0)">一级菜单A_8</a>
<a href="javascript:void(0)">一级菜单A_9</a>
</ul>
<h2 onClick="javascript:ShowMenu(this,1)"><a href="javascript:void(0)">+ 一级菜单A_2</a></h2>
<ul class="no">
<a href="javascript:void(0)">一级菜单A_0</a>
<a href="javascript:void(0)">一级菜单A_1</a>
<a href="javascript:void(0)">一级菜单A_2</a>
<a href="javascript:void(0)">一级菜单A_3</a>
<a href="javascript:void(0)">一级菜单A_4</a>
<a href="javascript:void(0)">一级菜单A_5</a>
<a href="javascript:void(0)">一级菜单A_6</a>
<a href="javascript:void(0)">一级菜单A_7</a>
<a href="javascript:void(0)">一级菜单A_8</a>
<a href="javascript:void(0)">一级菜单A_9</a>
</ul>
<h2 onClick="javascript:ShowMenu(this,2)"><a href="javascript:void(0)">+ 一级菜单A_3</a></h2>
<ul class="no">
<a href="javascript:void(0)">一级菜单A_0</a>
<a href="javascript:void(0)">一级菜单A_1</a>
<a href="javascript:void(0)">一级菜单A_2</a>
<a href="javascript:void(0)">一级菜单A_3</a>
<a href="javascript:void(0)">一级菜单A_4</a>
<a href="javascript:void(0)">一级菜单A_5</a>
<a href="javascript:void(0)">一级菜单A_6</a>
<a href="javascript:void(0)">一级菜单A_7</a>
<a href="javascript:void(0)">一级菜单A_8</a>
<a href="javascript:void(0)">一级菜单A_9</a>
</ul>
<h2 onClick="javascript:ShowMenu(this,3)"><a href="javascript:void(0)">+ 一级菜单A_4</a></h2>
<ul class="no">
<a href="javascript:void(0)">一级菜单A_0</a>
<a href="javascript:void(0)">一级菜单A_1</a>
<a href="javascript:void(0)">一级菜单A_2</a>
<a href="javascript:void(0)">一级菜单A_3</a>
<a href="javascript:void(0)">一级菜单A_4</a>
<a href="javascript:void(0)">一级菜单A_5</a>