function switchLayer(id, no, length, aid) {
  for(var i=1; i<=length; i++) {
	document.getElementById(id+i).style.visibility = "hidden";
        document.getElementById(aid+i).style.fontWeight = 'normal';
        document.getElementById(aid+i).style.color = '#888888';
   }
   document.getElementById(id+no).style.visibility = "visible";
   document.getElementById(aid+no).style.fontWeight = "bold";
   document.getElementById(aid+no).style.color = "#FF9500";
}