listbox如何添加数据??? --高分求救!!!

<html><head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<meta name="GENERATOR" content="Microsoft FrontPage 4.0">
<meta name="ProgId" content="FrontPage.Editor.Document">
<title>New Page 1</title>
<SCRIPT LANGUAGE="JavaScript">
<!--
  function d(){
      form1.viFlag.options[form1.viFlag.length]=new Option(form1.S1.value,"sdfsdF");
}
//-->
</SCRIPT>
</head><body><form method="POST" name="form1" action="--WEBBOT-SELF--">
  <!--webbot bot="SaveResults" U-File="fpweb:///_private/form_results.txt"
  S-Format="TEXT/CSV" S-Label-Fields="TRUE" -->
  <p><select size="1" name="viFlag">
    <option value="1">呆帐</option>
    <option value="2">坏账</option>
  </select><textarea rows="2" name="S1" cols="20"></textarea><input type="button" value="按钮" name="B1" onclick="d()"></p>
</form></body></html>