var how_many_ads = 4;
var now = new Date()
var sec = now.getSeconds()
var ad = sec % how_many_ads;
ad +=1;
if (ad==1) {                   
url="index.htm"   
alt="权威，翔实，及时教育信息尽在“世纪教育”";
banner="images/780X120.swf"
width="780";     
height="120";    
type=2
}

if (ad==2) {                   
url="index.htm"   
alt="权威，翔实，及时教育信息尽在“世纪教育”";
banner="images/banner2.swf"
width="780";     
height="120";    
type=2
}

if (ad==3) {                   
url="index.htm"   
alt="权威，翔实，及时教育信息尽在“世纪教育”";
banner="images/ad_main.gif"
width="780";     
height="120";    
type=1
}
if (ad==4) {                   
url="index.htm"   
alt="权威，翔实，及时教育信息尽在“世纪教育”";
banner="images/banner.swf"
width="780";     
height="120";    
type=2
}

if (type==2){
document.writeln('<center>');
document.writeln('<object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=5,0,0,0" width="780" height="120"><param name=movie');
document.writeln('value=\"' + banner + '\"><param name=quality value=high>');
document.writeln('<embed src=\"' + banner + '\" quality=high pluginspage="http://www.macromedia.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash" type="application/x-shockwave-flash" width="780" height="120"></embed></object>')
document.writeln('</center>');
}
if (type==1){
document.writeln('<center>');
document.writeln('<a href=\"' + url + '\" target=\"_blank\">');
document.writeln('<img src=\"' + banner + '\" width=');
document.writeln(width + ' height=' + height + ' ');
document.writeln('alt=\"' + alt + '\" border=0><br>');
document.writeln('</a></center>');
}