以下循环队列的实现方式中，长度为n的队列，所能容纳的元素个数也为n的有: In the following realizing ways of circular queue, the queue whose length is n can also contain the number of n elements is:（There are more than one answers.）

A、只用front和rear两个指针标记队列的头和尾，两个指针均为实指Only use front and rear as the queue’s head and tail pointers and the two pointers are actually referring to.

B、用front和rear两个指针标记队列的头和尾，并用整型变量len记录队列元素数With the queue’s head and tail pointers marked as front and rear, use the integer variable len to record the number of elements.

C、用front和rear两个指针标记队列的头和尾，并用布尔型变量empty记录队列是否为空With the queue’s head and tail pointers marked as front and rear, use Boolean variable empty record whether the queue is empty.

D、只用front和rear两个指针标记队列的头和尾，两个指针均为虚指Only use front and rear as the queue’s head and tail pointers and the two pointers are virtually referring to.