timer = null;

function hideMenus(){
  timer = setTimeout("nowHideMenus()",1000);
}

function nowHideMenus(){
  document.getElementById("menua").style.display="none";
  document.getElementById("menub").style.display="none";
  document.getElementById("menuc").style.display="none";
}

function showMenu(key){
    clearTimeout(timer);
    nowHideMenus();
    document.getElementById("menu"+key).style.display="";
}