案例：Bootstrap案例     状态：可编辑再运行    进入竖版
 运行结果　
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<!DOCTYPE html>
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<html>
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<head>
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    <meta charset="utf-8">
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    <title>Bootstrap 实例 - 下拉菜单（Dropdowns）</title>
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    <link rel="stylesheet" href="/css/bootstrap/bootstrap3.3.7.min.css">
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    <script src="/js/bootstrap/jquery.min.js"></script>
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    <script src="/js/bootstrap/bootstrap3.3.7.min.js"></script>
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</head>
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<body>
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​
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<div class="dropdown">
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    <button type="button" class="btn dropdown-toggle" id="dropdownMenu1"
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            data-toggle="dropdown">
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        主题
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        <span class="caret"></span>
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    </button>
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    <ul class="dropdown-menu" role="menu" aria-labelledby="dropdownMenu1">
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        <li role="presentation">
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            <a role="menuitem" tabindex="-1" href="#">Java</a>
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        </li>
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        <li role="presentation">
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            <a role="menuitem" tabindex="-1" href="#">数据挖掘</a>
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        </li>
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        <li role="presentation">
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            <a role="menuitem" tabindex="-1" href="#">数据通信/网络</a>
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        </li>
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        <li role="presentation" class="divider"></li>
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        <li role="presentation">
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            <a role="menuitem" tabindex="-1" href="#">分离的链接</a>
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        </li>
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    </ul>
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</div>
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​
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</body>
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</html>