<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="//cdn.bootcss.com/bootstrap/3.3.6/css/bootstrap.min.css">
<script src="//cdn.bootcss.com/jquery/2.1.1/jquery.min.js"></script>
<script src="//cdn.bootcss.com/bootstrap/3.3.6/js/bootstrap.min.js"></script>
<p> .caret 类显示了一个下拉的功能: <span class="caret"></span></p>
<button type="button" class="btn btn-primary dropdown-toggle" data-toggle="dropdown">Menu <span class="caret"></span></button>
<ul class="dropdown-menu" role="menu">
<li><a href="#">一个链接</a></li>
<li><a href="#">另一个链接 link</a></li>
<li><a href="#">其他功能</a></li>