function cambiar(id){
         var obj = document.getElementById(id);
         if(obj.style.display == 'block') obj.style.display = 'none';
         else obj.style.display = 'block';
      }
      function quitar(id){
         var obj = document.getElementById(id);
         obj.style.display = 'none';
      }
      function poner(id){
         var obj = document.getElementById(id);
         obj.style.display = 'block';
      }