Amusement parks make most of their money from admission fees paid by guests attending the park. Other sources include parking fees, food and drink sales and souvenirs. Practically all amusement parks operate using one of two admission principles:         Pay-as-you-go In this form, a guest enters the park at little or no charge. The guest must then buy rides one by one, either at the attraction's entrance or by buying ride tickets. The cost of the attraction is often based on its complexity   or popularity. The park may allow guests to buy unlimited admissions to all attractions within the park. A pass is then shown at the attraction entrance to gain admission.        Disneyland opened in 1955 using the pay-as-you-go form. Initially, guests paid the ride admission fees at the attractions. Soon, the problems of dealing with so many coins led to the development of a ticket system that, while now out of use, is still part of the amusement-park vocabulary. In this new form, guests bought ticket books that contained a number of tickets, with "A," "B" and "C." Rides and attractions using an "A-ticket" were generally simple, with "B-tickets" and "C-tickets" used for the larger, more popular rides. Later, the "D-ticket" was added, then finally the now-famous "E-ticket," which was used for the biggest rides, like Space Mountain. Smaller tickets could be traded up for use on larger rides. Disneyland, as well as the Magic Kingdom at Walt Disney World, gave up this practice in 1982.        The advantages include:        guests pay for only what they choose to experience         attraction costs can be changed easily         The disadvantages include:        guests may get tired of spending money almost continuously         guests may not spend as much on food or souvenirs What would be introduced following the passage?
The other admission principle. Amusement parks' earnings. Some other admission principles. Users of the pay-as-you-go principle.
Question: Amusement parks make most of their money from admission fees paid by guests attending the park. Other sources include parking fees, food and drink sales and souvenirs. Practically all amusement parks operate using one of two admission principles:         Pay-as-you-go In this form, a guest enters the park at little or no charge. The guest must then buy rides one by one, either at the attraction's entrance or by buying ride tickets. The cost of the attraction is often based on its complexity   or popularity. The park may allow guests to buy unlimited admissions to all attractions within the park. A pass is then shown at the attraction entrance to gain admission.        Disneyland opened in 1955 using the pay-as-you-go form. Initially, guests paid the ride admission fees at the attractions. Soon, the problems of dealing with so many coins led to the development of a ticket system that, while now out of use, is still part of the amusement-park vocabulary. In this new form, guests bought ticket books that contained a number of tickets, with "A," "B" and "C." Rides and attractions using an "A-ticket" were generally simple, with "B-tickets" and "C-tickets" used for the larger, more popular rides. Later, the "D-ticket" was added, then finally the now-famous "E-ticket," which was used for the biggest rides, like Space Mountain. Smaller tickets could be traded up for use on larger rides. Disneyland, as well as the Magic Kingdom at Walt Disney World, gave up this practice in 1982.        The advantages include:        guests pay for only what they choose to experience         attraction costs can be changed easily         The disadvantages include:        guests may get tired of spending money almost continuously         guests may not spend as much on food or souvenirs What would be introduced following the passage?
A. The other admission principle.
B. Amusement parks' earnings.
C. Some other admission principles.
D. Users of the pay-as-you-go principle.
Answer: