JavaScript获取select值动态修改span标签内容

<script type="text/javascript"><!--mce:0--></script>
<select id="AdType"> <option selected="selected" value="*200*100">左边广告</option> <option value="95*60">右边广告</option> <option value="500*235">强打广告</option> <option value="160*80">醒目广告</option></select>
 
<span id="show">我</span>

<script LANGUAGE="JavaScript">
m=5
 
Time=window.setInterval("Alors()",1000);
function Alors(){
            Ob=document.getElementById("L");
                        Ob.innerHTML=m;
                        m--;
                        if(m==0){
                          window.open('Logon.aspx','_self');
                        }
 
}
</script>
 
<span id="L">5</span>