二级下拉菜单下沉，大神进来看看
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>等分按钮</title>
<link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css">
<link rel="stylesheet" href="style.css">
<style>
body{
margin-left:150px;
margin-top:200px;
}
</style>
</head>
<body>
<ul class="nav nav-pills">
<li class="active"><a href="##">首页</a></li>
<li class="dropdown">
<a href="##" class="dropdown-toggle" data-toggle="dropdown">教程<span class="caret"></span></a>
<ul class="dropdown-menu">
<li><a href="##">CSS3</a></li>
<li><a href="##">Sass</a></li>
<li><a href="##">jQuery</a></li>
<li><a href="##">Responsive</li>
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</body>
</html>
二级菜单一样的代码为什么《关于我们》那一列却下沉了呢？
