index.html

<li class="dropdown">
  <a href="#" class="dropdown-toggle" data-toggle="dropdown">About<b class="caret"></b></a>
  <span class="dropdown-arrow"></span>
    <ul class="dropdown-menu">
      <li><a href="about.html">About</a></li>
      <li><a href="team.html">Team</a></li>
      <li><a href="contact.html">Contact</a></li>
    </ul>
</li>