<!-- Single button -->

<div class="btn-group">

  <button type="button" class="btn btn-Default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">

    Action <span class="caret"></span>

  </button>

  <ul class="dropdown-menu">

    <li><a href="#">Action</a></li>

    <li><a href="#">Another action</a></li>

    <li><a href="#">Something else here</a></li>

    <li role="separator" class="divider"></li>

    <li><a href="#">Separated link</a></li>

  </ul>

</div>

<!-- Single button -->

<div class="btn-group">

  <button type="button" class="btn btn-danger">Action</button>

  <button type="button" class="btn btn-danger dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">

    <span class="caret"></span>

    <span class="sr-only">Toggle Dropdown</span>

  </button>

  <ul class="dropdown-menu">

    <li><a href="#">Action</a></li>

    <li><a href="#">Another action</a></li>

    <li><a href="#">Something else here</a></li>

    <li role="separator" class="divider"></li>

    <li><a href="#">Separated link</a></li>

  </ul>

</div>

   <div class="btn-group dropup">

      <button type="button" class="btn btn-default dropdown-toggle"  data-toggle="dropdown">  默认 <span class="caret"></span></button>

      <ul class="dropdown-menu" role="menu">

         <li><a href="#">功能</a></li>

         <li><a href="#">另一个功能</a></li>

         <li><a href="#">其他</a></li>

         <li class="divider"></li>

         <li><a href="#">分离的链接</a></li>

      </ul>

   </div>

   <div class="btn-group dropup">

      <button type="button" class="btn btn-primary dropdown-toggle"  data-toggle="dropdown">  原始 <span class="caret"></span>      </button>

      <ul class="dropdown-menu" role="menu">

         <li><a href="#">功能</a></li>

         <li><a href="#">另一个功能</a></li>

         <li><a href="#">其他</a></li>

         <li class="divider"></li>

         <li><a href="#">分离的链接</a></li>

      </ul>

   </div>