刚看的js，自己敲得时候就是不知道怎么回事 求解答啊。。

<title>无标题文档</title>
<script>

document.getElementById("link").onmouseclick = show;
document.getElementById("link").onmouseout = hide;
alert('欢迎光临本界面！！');
function show(){
alert(1);
}

function show(){
document.getElementById("ul1").style.onmouseover = 'block';
document.getElementById("link").style.background = 'yellow';
}
function hide(){
document.getElementById('ul1').style.display = 'none';
document.getElementById("link").style.background = 'yellow';
}
</script>
<style type="text/css">
.lis {
width:80px;
height:30px;
border:1px solid #000000;
position:relative;
width:100px;
list-style:none;
}
.lis a {
display:block;
line-height:30px;
text-align:center;
text-decoration:none;
}
ul ul {
margin:0px;
padding:0px;
border:1px solid #000000;
width:100px;
left:-1px;
top:30px;
background:#FFFF66;
visibility:hidden;
}
ul ul li {
text-align:center;
line-height:20px;
list-style:none;
width:40px;
}
</style>
</head>
<body>
<div>
<ul>
<li class="lis"> <a href="#" id="link">choose one</a></li>
<ul>
<li>dear</li>
<li>darling</li>
<li>sweetheart</li>
</ul>
</ul>
</div>
</body>
</html>