高分求关联菜单，200分

<HTML>
<HEAD>
<META http-equiv=Content-Type content="text/html; charset=gb2312">
<title>两级关联菜单</title>
</HEAD>
<BODY>
<SCRIPT LANGUAGE=javascript>
<!--
var prv=new Array()//品牌
var cty=new Array()//规格
var ctyid=new Array()//id
var ctyunit=new Array()//单位
function init(){

prv[0]="11111";

cty[0]=new Array()
ctyid[0]=new Array()
ctyunit[0]=new Array()

cty[0][0]="11-1";
ctyid[0][0]="334";
ctyunit[0][0]="111";

prv[1]="32";

cty[1]=new Array()
ctyid[1]=new Array()
ctyunit[1]=new Array()

cty[1][0]="324-23";
ctyid[1][0]="297";
ctyunit[1][0]="34";

prv[2]="test";

cty[2]=new Array()
ctyid[2]=new Array()
ctyunit[2]=new Array()

cty[2][0]="test-test";
ctyid[2][0]="335";
ctyunit[2][0]="test";




if(prv.length >0){
for(i=0;i<prv.length;i++)
with(document.frm.province)options[length]=new Option(prv[i],prv[i])
document.frm.province.onchange=new Function("go(this.selectedIndex)")
}
}

function go(sIndex){
with(document.frm.city){
length=0;
if(sIndex==0){options[0]=new Option("请选择");return}
for(i=0;i<cty[sIndex-1].length;i++)
options[length]=new Option(cty[sIndex-1][i],ctyid[sIndex-1][i])
document.frm.r.value=value;
}
}
window.onload=init
-->
</SCRIPT>
<form name=frm>
<SELECT name=province>
<OPTION selected>请选择</OPTION>
</SELECT>
<SELECT name=city onchange="r.value=value">
<OPTION selected>请选择</OPTION>
</SELECT>
<input name=r id=r>

<input name=u id=u>
</form>
</BODY>
</HTML>



要求，选择2级菜单后，代入对应的ctyunit值给u