In January of each year, the Sunny Hotel holds a very popular Carnival. Tickets must be ordered and paid for in advance, and are typically sold out by December of the preceding year. The realization principle indicates that the revenue from these ticket sales should be recognized in the period:
选项：

A:When the ticket is ordered;
B:When the Carnival is held;
C:When the cash are received;
D:When the ticket is sold