public Marcas getMarca(int id)
{
Marcas cat = new Marcas();
DataTable tabla = ds.ObtenerTabla("Marcas", "Select * from MARCAS where id_marca=" + id);
cat.setid_marca(Convert.ToInt32(tabla.Rows[0][0].ToString()));
cat.setNombre(tabla.Rows[0][1].ToString());
return(cat);
}