<html>
<head>
<!--禁止页面缓存-->
<meta http-equiv="content-type" content="text/html;charset=utf-8" />
<META HTTP-EQUIV="Pragma" CONTENT="no-cache">
<META HTTP-EQUIV="Cache-Control" CONTENT="no-cache">
<META HTTP-EQUIV="Expires" CONTENT="0">
</head>
<select id="ss">
<option >aa0</option>
<option >aa1</option>
<option >aa2</option>
<option >aa3</option>
</select>
<body>
<script >
var ss = document.getElementById('ss');
ss[3].selected = true;//选中
</script>
</html>