<div class="dropdown">
      <button class="btn dropdown-toggle" id='drop1' data-toggle="dropdown">
        帮助<span class="caret"></span>
      </button>
      <ul class="dropdown-menu" role="menu" aria-labelledby="drop1">
        <li role="presentation">
          <a role="menuitem" tabindex="-1" href="#"> 关于我们 </a>
        </li>
        <li role="presentation">
          <a role="menuitem" href="#"> 关于我们 </a>
        </li>
        <li role="presentation">
          <a role="menuitem" href="#"> 关于我们 </a>
        </li>
        <li role="presentation">
          <a role="menuitem" href="#"> 关于我们 </a>
        </li>
      </ul>
    </div>

<div class="btn-group" role="toolbar">
  <div class="btn-group btn-group-lg">
    <button type="button" class="btn btn-default">按钮 1</button>
    <button type="button" class="btn btn-default">按钮 2</button>
    <button type="button" class="btn btn-default">按钮 3</button>
  </div>
    <div class="btn-group btn-group-sm">
    <button type="button" class="btn btn-default">按钮 4</button>
    <button type="button" class="btn btn-default">按钮 5</button>
    <button type="button" class="btn btn-default">按钮 6</button>
  </div>
    <div class="btn-group btn-group-xs">
    <button type="button" class="btn btn-default">按钮 7</button>
    <button type="button" class="btn btn-default">按钮 8</button>
    <button type="button" class="btn btn-default">按钮 9</button>
  </div>
</div>

<div class="btn-group">
  <button type="button" class="btn btn-default dropdown-toggle btn-lg" 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>