这个JS哪里错了？

<form name="form1" method="post" action="">
<table width="163" border="1">
<tr>
<td width="45">name</td>
<td width="102">

<select name="select1" disabled>
<option value="">wo</option>
<option value="">ni</option>
</select>

</td>
</tr>
<tr>
<td>sex </td>
<td>

<select name="select2">
<option>男</option>
<option>女</option>
</select>

</td>
</tr>
<tr>
<td colspan="2"><div align="center">
<input type="submit" name="Submit" value="提交">
</div></td>
</tr>
</table>
</form>
<script language="JavaScript">
function show()
{
if(document.form1.select1.disabled==true){
document.form1.select2.disabled=true;

}
else
{
document.form1.select2.disabled=false;
}
}
show();
</script>

把脚本放下边,放前边当然没对象了,FORM1还没下载下来呢.

up楼上的