求救！！！

下面的一段代码到底有什么问题，大家能帮我看看吗？

<form action="b2_a.asp?PageN=2&SPN=0" method="POST" name=xx >

<script language=JavaScript>
<!--
function aa2(aa)
{
for (var i = document.xx.a2.options.length; i >= 1; i--){
document.xx.a2.options[i] = null;
document.xx.a2.options[0].selected;
}

for (var i = document.xx.a3.options.length; i >= 1; i--){
document.xx.a3.options[i] = null;
document.xx.a3.options[0].selected;
}

if(aa.options[aa.selectedIndex].value='1'){
document.xx.a2.options[document.xx.a2.length] = new Option('材料厂商','3');
}
if(aa.options[aa.selectedIndex].value='2'){
document.xx.a2.options[document.xx.a2.length] = new Option('个人会员','4');
document.xx.a2.options[document.xx.a2.length] = new Option('政府机构','5');
document.xx.a2.options[document.xx.a2.length] = new Option('建设单位','6');
document.xx.a2.options[document.xx.a2.length] = new Option('施工企业','7');
document.xx.a2.options[document.xx.a2.length] = new Option('设计单位','8');
document.xx.a2.options[document.xx.a2.length] = new Option('监理单位','9');
document.xx.a2.options[document.xx.a2.length] = new Option('咨询公司','10');
document.xx.a2.options[document.xx.a2.length] = new Option('其他单位','11');
}
}

function aa3(bb)
{
for (var i = document.xx.a3.options.length; i >= 1; i--){
document.xx.a3.options[i] = null;
document.xx.a3.options[0].selected;
}
if(bb.options[bb.selectedIndex].value='1'){
document.xx.a3.options[document.xx.a3.length] = new Option('自主维护厂商','12');
document.xx.a3.options[document.xx.a3.length] = new Option('自主申请厂商','13');
document.xx.a3.options[document.xx.a3.length] = new Option('网上上传厂商','14');
}
if(bb.options[bb.selectedIndex].value='2'){
document.xx.a3.options[document.xx.a3.length] = new Option('钻石会员','15');
document.xx.a3.options[document.xx.a3.length] = new Option('白金会员','16');
document.xx.a3.options[document.xx.a3.length] = new Option('试用会员','17');
document.xx.a3.options[document.xx.a3.length] = new Option('自主注册会员','18');
}
}
-->
</script>
<font size="2">会员分类:<select name=a1 onchange=aa2(this)>
<option value=0 selected>全　　部</option>
<option value=1>供应厂商</option>
<option value=2>非供应厂商</option>
</select><br>
分类类别:<select name=a2 onchange=aa3(this)>
<option value=0 selected>全　　部</option>
</select><br>
会员级别:
<select name=a3 >
<option value=0 selected>全　　部</option>
</select>
</font>