【单选题】
假定一个循环顺序队列的队首和队尾指针分别为f和r,则判断队空的条件是()
A、f+1==r
B、r+1==f
C、f==0
D、f==r
A、f+1==r
B、r+1==f
C、f==0
D、f==r
A、A. front = =rear B、B. (front-1)%n= =rear C、C. (rear+1)%n= =front D、D. (rear-1)%n= = front