如何动态添加select控件内容，并绑定相应的value值

[yzhouen]

现在有select控件，id为pid：
<td noWrap><select id="pid" style="WIDTH: 100px" runat="server"
<option selected></option>
</select> </td>

想动态的将一个数组的内容添加到其中作为下拉项
var a=new Array("中国","美国","英国","朝鲜","韩国");
var b=new Array("0","1","2","3","4");
怎样将这些值插入其中，并且使b数组中的值作为它的各项的value值？
用javascript

[xiaohuasz]

<table>
<td noWrap>
<select id="pid" style="WIDTH: 100px" runat="server"
<option selected></option>
<script language=javascript>
var a=new Array("中国","美国","英国","朝鲜","韩国");
var b=new Array("0","1","2","3","4");
for(i=0;i<a.length;i++)
document.write("<option value="+b[i]+">"+a[i]+"</option>")
</script>
</select>
</td>
</table>

[ccp]

<select id="pid" style="WIDTH: 100px" runat="server"
<option selected></option>
</select>
<script language="javascript">
var a=new Array("中国","美国","英国","朝鲜","韩国");
var b=new Array("0","1","2","3","4");

for(i=0;i<a.length;i++)
{
var opt = document.createElement("option");
opt.text=a[i];
opt.value=b[i];
pid.add(opt);
}

</script>

[yzhouen]

如果第二次执行如何清除第一次的结果，就是将pid中的所有项删除然后在重新绑定？