addClass adds white space.

addClass adds white space.

when  addClass('choose') to li, there is always a white space right under it. anybody know the reason and how to solve it? thanks in advance.
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<!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" />
<script type="text/javascript" src="demo_inc/jQuery.js"></script>
<title>无标题文档</title>
<style>
body{
font-family:Arial, Helvetica, sans-serif}

li{
margin-left:5px;
font-size:12px;
list-style:none;
float:left;
text-align:center;


}
.choose{
display:block;
border:solid 1px;
}
</style>
<script>
$(document).ready(function(){

$("div li").mouseover(function(){
    $(this).css('cursor','pointer');
})


$("div li").click(function(){
    $(this).addClass('choose');
   
})



})
</script>
</head>

<body>               
   
   
    <div style="width:148px; min-height:100px;display:block; border:solid 1px; position:relative;">
       
        <li>Div 01-01</li>
        <li>Div 01-02</li>
        <li>Div 01-03</li>
        <li>Div 01-04</li>
        <li>Div 01-01</li>
        <li>Div 01-02</li>
        <li>Div 01-03</li>
        <li>Div 01-04</li>
    </div>
    <div style="width:348px; min-height:100px;display:block; border:solid 1px; position:relative;">
        <li>Div 01-01</li>
        <li>Div 01-02</li>
        <li>Div 01-03</li>
        <li>Div 01-04</li>
        <li>Div 01-01</li>
        <li>Div 01-02</li>
        <li>Div 01-03</li>
        <li>Div 01-04</li>
    </div>
       
   
</body>


</html>