js 修改 select 选中

<SCRIPT LANGUAGE="JavaScript">
<!--
function check(c,k)
{
for (var i=0;i<c.options.length ;i++ )
{

if (c.options(i).value==k)
{
c.selectedIndex =i;
break;
}
}
}
//-->
</SCRIPT>

<FORM METHOD=POST ACTION="" name="myform">
<SELECT NAME="hehe">
    <OPTION VALUE="北京" SELECTED>北京</option>
    <OPTION VALUE="上海">上海</option>
           <OPTION VALUE="桂林">桂林</option>
     <OPTION VALUE="广州">广州</option>
     <OPTION VALUE="成都">成都</option>
</SELECT>
    </FORM>
    <INPUT TYPE="button" NAME="" value="改变" onclick="check(document.myform.hehe,'桂林')">