title: Bootstrap navbar dropdown does not open
body: <p>The dropdown menu in the navbar which build by bootstrap does not open.
  <br> Do you have any solutions?
  <br> here is the code:</p>
  
  <pre><code>&lt;head&gt;
      &lt;meta charset="utf-8"&gt;
      &lt;meta http-equiv="X-UA-Compatible" content="IE=edge"&gt;
      &lt;meta name="viewport" content="width=device-width, initial-scale=1"&gt;
          &lt;!-- Latest compiled and minified CSS --&gt;
          &lt;link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css"&gt;
  
          &lt;!-- Optional theme --&gt;
          &lt;link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap-theme.min.css"&gt;
  
          &lt;!--JQuery.min.js------------&gt;
          &lt;script src="http://code.jquery.com/jquery.min.js"&gt;&lt;/script&gt; 
          &lt;!--JQuery.min.js------------&gt;
  
  
          &lt;!-- Latest compiled and minified JavaScript --&gt;
          &lt;script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"&gt;&lt;/script&gt;
      &lt;link href="style.css" rel="stylesheet"&gt;
  &lt;/head&gt;
  </code></pre>