The cabins of domestic passenger tickets are mainly divided into first class (cabin code F), business class (cabin code C) and economy class (cabin code Y). There are different seating classes in economy class (cabin codes are B, K, H, L, M, Q, X, E, and each airline has different logos and different prices). Although these prices belong to economy class, the service enjoyed by the lower class is not the same as that enjoyed by the higher class. The most obvious thing is to book the seats and meals on the plane in advance (meaning that even if the seats and meals are booked in advance, there are very low cabins that cannot be refunded.