说明：  模拟餐馆点菜系统。 你可以到一个餐馆去仔细研究一下餐馆的业务流程：餐馆事先准备好自己的招牌菜及一些常规的菜式，有营业场所，服务人员等；顾客来了以后，服务生先给客人找一张桌子坐下来，然后递上菜谱等待顾客点菜，顾客可以点一个菜，也可以退菜，完了之后结账走人，这张桌子又可以用来招待下一批顾客。
(Analog system a la carte restaurant. You can go to a restaurant to look at business processes restaurants: the restaurant in advance to prepare their signature dishes and some conventional dishes, there are business premises, service personnel customers came after the staff give the guests to find a sit down the table, and then wait for customers to order and handed the menu, customers can point a dish, vegetables can also be returned, then leave after the closing, this table can be used to entertain the next batch of customers.)