<body>
<!-- jQuery first, then Bootstrap JS. -->
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.4/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.2/js/bootstrap.min.js" integrity="sha384-vZ2WRJMwsjRMW/8U7i6PWi6AlO1L79snBrmgiDpgIWJ82z8eA5lenwvxbMV1PAh7" crossorigin="anonymous"></script>
<ul class="nav nav-tabs">
<li class="active"><a href="#">Home</a></li>
<li class="dropdown">
<a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button">Products</a>
<ul class="dropdown-menu">
<li><a href="#">one</a></li>
<li><a href="#">two</a></li>
<li><a href="#">three</a></li>
</ul>
</li>
<li><a href="#">Contact</a></li>
</ul>
</body>
这是正文部分中的代码。你们能帮我弄清楚出了什么问题吗？我无法看到水平选项卡中的内容:(