导航栏按钮不会下拉

Question

我是一名初级网络开发人员，我正在为我的下拉按钮而苦苦挣扎。当我调整屏幕大小进行测试时，它不会下拉。谢谢！

<nav class="navbar navbar-expand-lg navbar-dark bg-dark static-top">
  <div class="container">
    <a class="navbar-brand" href="#">
          <img src="http://placehold.it/150x50?text=Logo" alt="">
        </a>
    <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarResponsive" aria-controls="navbarResponsive" aria-expanded="false" aria-label="Toggle navigation">
          <span class="navbar-toggler-icon"></span>
        </button>
    <div class="collapse navbar-collapse" id="navbarResponsive">
      <ul class="navbar-nav ml-auto">
        <li class="nav-item active">
          <a class="nav-link" href="#">Home
                <span class="sr-only">(current)</span>
              </a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="about.html">About</a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="services.html">Services</a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="contact.html">Contact</a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="form.html">Sign In/Sign Up</a>
        </li>
      </ul>
    </div>
  </div>
</nav>

Answer 1

你声明了吗？

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>
<script src="//netdna.bootstrapcdn.com/bootstrap/3.1.1/js/bootstrap.min.js"></script>
<link rel="stylesheet" type="text/css" href="//netdna.bootstrapcdn.com/bootstrap/3.1.1/css/bootstrap.min.css">