为什么二级菜单无法显示？
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>下拉菜单2-1，JS</title>
<style>
* {
padding: 0;
margin: 0;
}
#nav {
background-color: #eee;
width: 600px;
height: 40px;
margin: 0 auto;
}
ul {
list-style: none;
}
ul li {
float: left;
line-height: 40px;
text-align: center;
}
a {
text-decoration: none;
color: #000;
display: block;
padding: 0 20px;
}
a:hover {
color: #fff;
background-color: #666;
}
ul li ul li {
float: none;
background-color: #eee;
margin-top: 2px;
}
ul li ul {
position: absolute;
display: none;
}
</style>
<script type="javascript">
function showsubmenu(){
var submenu=li.getElementsByTagName("ul")[0];
submenu.style.display="block";
}
function hidesubmenu(){
var submenu=li.getElementsByTagName("ul")[0];
submenu.style.display="none";
}
</script>
</head>
<body>
<div id="nav">
<ul>
<li><a href="#">首页</a></li>
<li onmouseover="showsubmenu()" onmouseout="hidesubmenu()"><a href="#">课程大厅</a>
<ul>
<li><a href="">javascript</a></li>
<li><a href="">jQuery</a></li>
</ul>
</li>
<li><a href="#">学习中心</a>
<ul>
<li><a href="">视频学习</a></li>
<li><a href="">案例学习</a></li>
<li><a href="">交流平台</a></li>
</ul>
</li>
<li><a href="#">经典案例</a></li>
<li><a href="#">关于我们</a></li>
</ul>
</div>
</body>
</html>
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1回答
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JavaScript