代码最少的随机图片广告代码

代码最少的随机图片广告代码。效果看上面的演示，刷新即可变换图片，符合W3C标准。
JS代码：
<script language="JavaScript" type="text/javascript">
tips = new Array(4);
tips[0] = '<a href="http://51xuediannao.com/" target="_blank"><img alt="懒人建站" width="970" height="90" src="03.jpg" border="0" /></a>';
tips[1] = '<a href="http://51xuediannao.com/JS" target="_blank"><img alt="JS代码-懒人建站" width="970" height="90" src="02.jpg" border="0" /></a>';
tips[2] = '<a href="http://51xuediannao.com/jd/ad" target="_blank"><img alt="广告代码-懒人建站" width="970" height="90" src="01.jpg" border="0" /></a>';
tips[3] = '<a href="http://51xuediannao.com/html+css" target="_blank"><img alt="HTML+CSS模板-懒人建站" width="970" height="90" src="03.jpg" border="0" /></a>';

index = Math.floor(Math.random() * tips.length);
document.write(tips[index]);
</script>