function ShowOne(cls){
 var ds=zxcByClassName(cls);
 var rnu=Math.floor(Math.random()*ds.length);
 for (var z0=0;z0<ds.length;z0++){
  ds[z0].style.display=z0!=rnu?'none':'block';
 }
}

function zxcByClassName(nme,el,tag){
 if (typeof(el)=='string') el=document.getElementById(el);
 el=el||document;
 for (var tag=tag||'*',reg=new RegExp('\\b'+nme+'\\b'),els=el.getElementsByTagName(tag),ary=[],z0=0; z0<els.length;z0++){
  if(reg.test(els[z0].className)) ary.push(els[z0]);
 }
 return ary;
}