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怎么没有反应？请教高手

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<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <title>使用fadeTo()方法设置淡入淡出效果的不透明度</title>
        <script src="http://libs.baidu.com/jquery/1.9.0/jquery.js" type="text/javascript"></script>
        <link href="style.css" rel="stylesheet" type="text/css" />
    </head>
    
    <body>
        <h3>使用fadeTo()方法设置淡入淡出效果的不透明度</h3>
        <span class="red"></span><span class="orange"></span><span class="blue"></span>
        
        <script type="text/javascript">
            $(function () {
                $("span").each(function (index) {
                    switch (index) {
                        case 0:
                            $("this").fadeTo(3000,0.2);
                            break;
                        case 1:
                            $("this").fadeTo(3000,0.4);
                            break;
                        case 2:
                           $("this").fadeTo(3000,0.6);
                            break;
                    }
                });
            });
        </script>
    </body>
</html>