var subs_array = new Array("sub1","sub2","sub3","sub3a","sub4","sub5","sub6","sub7","sub8","sub9","sub10","sub11","sub12","sub13","sub14","sub15","sub16","sub17","sub18","sub19","sub20","sub21");// Put the id's of your hidden divs in this array

function displaySubs(the_sub){
	 if (document.getElementById(the_sub).style.display==""){
	   document.getElementById(the_sub).style.display = "none";return
  }
  for (i=0;i<subs_array.length;i++){
	   var my_sub = document.getElementById(subs_array[i]);
	   my_sub.style.display = "none";
	 }
  document.getElementById(the_sub).style.display = "";
}