二级关联菜单

<form name="doublecombo">
    <p>
    <select name="example" size="1" onChange="redirect(this.options.selectedIndex)">
        <option>国外JavaScript技术网站</option>
        <option>国内JavaScript技术网站</option>
        <option>国外的著名搜索引擎</option>
    </select>
    <select name="stage2" size="1">
        <option value="http://wsabstract.com">Website Abstraction</option>
        <option value="http://www.dynamicdrive.com">Dynamicdrive.com</option>
        <option value="http://javascript.internet.com">JavaScript</option>
    </select>
    <input type="button" name="test" value="Go!" onClick="go()">
    </p>
</form>

<script>
<!-- 
    var groups=document.doublecombo.example.options.length
    var group=new Array(groups)
    for (i=0; i<groups; i++)
    group[i]=new Array()
    group[0][0]=new Option("Website Abstraction","http://wsabstract.com")
    group[0][1]=new Option("Dynamicdrive.com","http://www.dynamicdrive.com")
    group[0][2]=new Option("JavaScript","http://javascript.internet.com")

    group[1][0]=new Option("万旭JavaScript仓库","http://www.wanxu.com")
    group[1][1]=new Option("JavaScript2000","http://www.javascript2000.com")
    group[1][2]=new Option("无忧脚本","http://www.51js.com")

    group[2][0]=new Option("Hotbot","http://www.hotbot.com")
    group[2][1]=new Option("Infoseek","http://www.infoseek.com")
    group[2][2]=new Option("Excite","http://www.excite.com")
    group[2][3]=new Option("Lycos","http://www.lycos.com")

    var temp=document.doublecombo.stage2
    function redirect(x)
>