谁会onmouseout鼠标离开事件

<style type="text/css">
.a{
width:400px;
height:100px;
border:1px solid #000;
}
.b{
width:900px;
height:150px;
border:1px solid #000;
background-color: #00FF00;
}
</style>
<script language="javascript">
function ok(num){
document.getElementById("rr").style.display="";
if(num==1){
document.getElementById("rr").className="a";
}
if(num==2){
document.getElementById("rr").className="b";
}
if(num==3){
document.getElementById("rr").style.display="none";
}
function out(){
document.getElementById("rr").style.display="none";
}
}
</script>
<a href="#"onMouseOver="ok(1)" onmouseout="out()" id="home">首页</a>
<a href=&q