请教，javascript与select的问题～～

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title> New Document </title>
<meta name="Generator" content="EditPlus">
<meta name="Author" content="">
<meta name="Keywords" content="">
<meta name="Description" content="">
<script language="JavaScript">
<!--
function ch(o)
{
if(o.selectedIndex==3)
{
document.all.fupload.style.display = '';
}
else
{
document.all.fupload.style.display = 'none';
}
}
//-->
</script>
</head><body>
<table>
<tr>
<td width="552" colspan="2"><select name="type" size="1" onpropertychange="ch(this);">
                            <option value="a">请选考验类型</option>
                            <option value="0">消息公告</option>
                            <option value="1">成绩查询</option>
                            <option value="2">试题下载</option>
                          </select></td><td height="55"> <div align="center" id ="fupload" style="display:none;"><font color="#FF0000"><strong>*</strong></font>上传文件：<input type="file" name="upload"></div></td>  </tr>
</table>

</body>
</html>