dropdown下拉列表是什么作用？怎么不能選中菜單?。?/h1>

<div class="dropdown">

? <button class="btn btn-default dropdown-toggle" type="button" id="dropdownMenu2" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">

? ? Dropup

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

? </button>

? <ul class="dropdown-menu" aria-labelledby="dropdownMenu2">

? ? <li? class="dropdown-header"><a href="#">蘋果</a></li>

? ? <li><a href="#">橘子/a></li>

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

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

? </ul>

</div>