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                        /基于bootstrap的網(wǎng)頁開發(fā)

求幫忙看一下為什么下拉菜單出不來？

<!DOCTYPE?html>
<html>
<head>
<meta?charset="utf-8">
<meta?http-equiv="X-UA-Compatible"?content="IE=edge">
<meta?name="viewport"?content="width=device-width,?initial-scale=1">
<title>Hello?World</title>
<link?>
</head>
<body>
<nav?class="navbar?navbar-default"?role="navigation">
??<div>
????<!--?Brand?and?toggle?get?grouped?for?better?mobile?display?-->
????<div>
??????<button?type="button"?class="navbar-toggle?collapsed"?data-toggle="collapse"?data-target="#bs-example-navbar-collapse-1">
????????<span>Toggle?navigation</span>
????????<span></span>
????????<span></span>
????????<span></span>
??????</button>
??????<a?href="#">某管理系統(tǒng)</a>
????</div>

????<!--?Collect?the?nav?links,?forms,?and?other?content?for?toggling?-->
????<div?class="collapse?navbar-collapse"?id="bs-example-navbar-collapse-1">
??????<ul?class="nav?navbar-nav">
????????<li><a?href="#">首頁</a></li>
????????<li?class="dropdown?active">
??????????<a?href="#"?data-toggle="dropdown">功能<span></span></a>
?????????<ul?role="menu"?aria-labelledby="dropdownMenu1">
????<li?role="presentation"><a?role="menuitem"?tabindex="-1"?href="#">Action</a></li>
????<li?role="presentation"><a?role="menuitem"?tabindex="-1"?href="#">Another?action</a></li>
????<li?role="presentation"><a?role="menuitem"?tabindex="-1"?href="#">Something?else?here</a></li>
????<li?role="presentation"><a?role="menuitem"?tabindex="-1"?href="#">Separated?link</a></li>
??</ul>
????????</li>
????????<li><a?href="#">幫助</a></li>
??????</ul>
??????<form?class="navbar-form?navbar-left"?role="search">
????????<div>
??????????<input?type="text"?placeholder="用戶名...">
????????</div>
????????<div>
??????????<input?type="password"?placeholder="密碼...">
????????</div>
????????<button?type="submit"?class="btn?btn-default">登錄</button>
??????</form>
??????
????</div><!--?/.navbar-collapse?-->
??</div><!--?/.container-fluid?-->
</nav>
<script?src="http://cdn.bootcss.com/jquery/1.11.1/jquery.min.js"></script>
<script?src="http://cdn.bootcss.com/bootstrap/3.2.0/js/bootstrap.min.js"></script>
</body>
</html>