tag=new Array();

tag[0]='<!-- Audiobook --><img src="common/images/topMainA.jpg" alt="" width="599" height="200" usemap="#mainA" />';
tag[1]='<!-- Book --><img src="common/images/topMainB.jpg" alt="" width="599" height="200" usemap="#mainB" />';

i=Math.floor(Math.random()*tag.length);
                  
document.write(tag[i]);