The following is some kind of data structure, which is implemented with two queues and supports adding and deleting elements:下面是某种数据结构，它用2个队列实现，支持添加、删除元素的操作：
When T is an integer, the following operations are performed sequentially on the initially empty data structure:当T为整数时，对初始为空的以上数据结构依次执行以下操作：
The only remaining elements in XXX at this time are:此时XXX中唯一剩下的元素是：
A2
B5
C7
D11