如何向列表框中添加内容?急!

Question

<form name=f>
<select name=s onchange="alert(this.value)">
<option value="aa">aa</option>
</selct>
<input type=button onclick="a()" value=add>
</form>
<script language=javascript>
var i=0
function a()
{
b=document.f.s
var opt=new Option("text"+ i,"value"+i,true,true)
b.options[b.options.length] = opt
i++
}
</script>

Answer 1

<select id=sel1></select>
<input id=str>
<button onclick="add()">add</button>
<script language="JavaScript">
<!--
function add(){
 var e=document.createElement("OPTION");
 e.value = str.value;
 e.innerText = str.value;
 sel1.appendChild(e);}
//-->
</script>

Answer 2

<select id="select1"></select>
<script language="JavaScript">
  var objOption = document.createElement("OPTION")
  select1.options.add(objOption)
  objOption.value = "选项的值"
  objOption.text = "显示的文本"
  
</script>

Answer 3

http://lucky.myrice.com/javascriptexam/add_del_Select.htm
http://lucky.myrice.com/javascriptexam/radioforselect.html