fetchPizzas()
  .then((pizzas) =＞ {
    return sortByToppings(pizzas)
      .then((pizzas) =＞ {
        return checkDeliveryOptions(pizzas)
          .then((pizzasWithDelivery) =＞ {
            return checkBirthdayGift(pizzasWithDelivery)
              .then((pizza) =＞ {
                return sendToCustomer(pizza);
              });
          });
      });
  });