为什么不出现下拉菜单
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN " "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd ">
<html xmlns= "http://www.w3.org/1999/xhtml ">
<head>
<meta http-equiv= "Content-Type " content= "text/html; charset=gb2312 " />
<title> 无标题文档 </title>
<style>
*{margin:0px;
padding:0px;}
#header{width:1000px;
background-imge:url();
background-repeat:repeat-x;
margin:0px auto;
}
#nav li{float:left;
position: relative;
list-style:none;
background-color:#9933CC; }
#nav li a{display:block;
background-color:#cdcdcd;
color:#000000;
margin-left:2px;
padding:1px;
width:100px;
height:20px;
text-decoration:none;}
#nav li a:hover{
background-color:#bbbbbb;
color:#ff0000;}
#nav li ul{display:none;
background-color:#33FF66;}
#nav li a:hover ul { display:block; position:absolute; left:0px;top:22px;}
#nav li a:hover ul li a { display:block;
background-color:#00FFCC;}
</style>
</head>
<body>
<div id=header> head </div>
<ul id= "nav ">
<li> <a href= "# "> 水平导航1 </a>
<ul>
<li> <a href= "# "> 下拉1-1 </a> </li>
<li> <a href= "# "> 下拉1-2 </a> </li>
<li> <a href= "# "> 下拉1-3 </a> </li>
<li> <a href= "# "> 下拉1-4 </a> </li>
<li> <a href= "# "> 下拉1-5 </a> </li>
</ul>
</li>
<li> <a href= "# "> 水平导航2 </a>
<ul>
<li> <a href= "# "> 下拉2-1 </a> </li>
<li> <a href= "# "> 下拉2-2 </a> </li>
<li> <a href= "# "> 下拉2-3 </a> </li>
<li> <a href= "# "> 下拉2-4 </a> </li>
<li> <a href= "# "> 下拉2-5 </a> </li>
</ul>
</li>
<li> <a href= "# "> 水平导航3 </a>
<ul>
<li> <a href= "# "> 下拉3-1 </a> </li>
<li> <a href= "# "> 下拉3-2 </a> </li>
<li> <a href= "# "> 下拉3-3 </a> </li>
<li&