r = 7; //随机数的范围
var seed = Math.random();
rnd = Math.ceil(seed * r); //产生随机数
   switch (rnd) {
   case 1:
       document.writeln("<div align=center>");
document.writeln("<iframe height=\'176\' width=\'950\' frameborder=\'no\' scrolling=\'no\' src= \'http:\/\/www.521lm.com\/code\/adview_pic1.php?r=1&c=8&w=950&h=176&b=0080ff&s=004080&bg=FFFFFF&p=808080&u=1540&at=p0&tt=t1\'><\/iframe>")
document.writeln("<\/div>")
       break;
   case 2:
       document.writeln("<div align=center>");
document.writeln("<iframe height=\'176\' width=\'950\' frameborder=\'no\' scrolling=\'no\' src= \'http:\/\/www.521lm.com\/code\/adview_pic2.php?r=1&c=8&w=950&h=176&b=0080ff&s=004080&bg=FFFFFF&p=808080&u=1540&at=p0&tt=t1\'><\/iframe>")
document.writeln("<\/div>")
       break;
   case 3:
       document.writeln("<div align=center>");
document.writeln("<iframe height=\'176\' width=\'950\' frameborder=\'no\' scrolling=\'no\' src= \'http:\/\/www.521lm.com\/code\/adview_pic4.php?r=1&c=8&w=950&h=176&b=0080ff&s=004080&bg=FFFFFF&p=808080&u=1540&at=p0&tt=t1\'><\/iframe>")
document.writeln("<\/div>")
       break;
   case 4:
       document.writeln("<div align=center>");
document.writeln("<iframe height=\'176\' width=\'950\' frameborder=\'no\' scrolling=\'no\' src= \'http:\/\/www.521lm.com\/code\/adview_pic5.php?r=1&c=8&w=950&h=176&b=0080ff&s=004080&bg=FFFFFF&p=808080&u=1540&at=p0&tt=t1\'><\/iframe>")
document.writeln("<\/div>")
       break;
   case 5:
       document.writeln("<div align=center>");
document.writeln("<iframe height=\'176\' width=\'950\' frameborder=\'no\' scrolling=\'no\' src= \'http:\/\/www.521lm.com\/code\/adview_pic_z.php?r=1&c=8&w=950&h=176&b=0080ff&s=004080&bg=FFFFFF&p=808080&u=1540&at=p0&tt=t1\'><\/iframe>")
document.writeln("<\/div>")
       break;
   case 6:
       document.writeln("<div align=center>");
document.writeln("<iframe height=\'176\' width=\'950\' frameborder=\'no\' scrolling=\'no\' src= \'http:\/\/www.521lm.com\/code\/adview_pic_m.php?r=1&c=8&w=950&h=176&b=0080ff&s=004080&bg=FFFFFF&p=808080&u=1540&at=p0&tt=t1\'><\/iframe>")
document.writeln("<\/div>")
       break;
   case 7:
       document.writeln("<div align=center>");
document.writeln("<iframe height=\'176\' width=\'950\' frameborder=\'no\' scrolling=\'no\' src= \'http:\/\/www.521lm.com\/code\/adview_pic_r.php?r=1&c=8&w=950&h=176&b=0080ff&s=004080&bg=FFFFFF&p=808080&u=1540&at=p0&tt=t1\'><\/iframe>")
document.writeln("<\/div>")
       default:
       break;
    }