求解 学bootstrap下面代码没有出现导航栏
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width,initial-scale=1">
<script src="jq/a.js"></script>
<link rel="stylesheet" href="//cdn.bootcss.com/bootstrap/3.3.5/css/bootstrap.min.css">
</head>
<body>
<nav class="navbar navbar-inverse navbar-fixed-top" role="navigation">
<div class="container">
<div class="navbar-header">
<a href="http://www.baidu.com" class="navbar-brand">百度一下</a>
</div>
<div id="navbar" class="collapse navbar-collapse">
<ul class="nav navbar-nav">
<li class="active"><a href="#">1</a></li>
<li>2</li>
<li>3</li>
</ul>
</div>
</div>
</nav>
</body>
</html>