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在火狐和谷歌中并沒有效果是怎么回事？求解

<div class="btn-group" role="group" >
???????????? <button type="button" class="btn btn-default">1</button>
???????????? <button type="button" class="btn btn-default">2</button>

????????????? <div class="btn-group" role="group">
?????????????????? <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
??????????????????????? Dropdown
??????????????????? <span class="caret"></span>
??????????????????? </button>
??????????????????? <ul class="dropdown-menu">
???????????????????????? <li><a href="#">Dropdown link</a></li>
???????????????????????? <li><a href="#">Dropdown link</a></li>
???????????????????? </ul>
????????????? </div>
????????? </div>