A.1,2,3,4 B.4,3,2,1 C.1,4,3,2 D.3,4,1,2
A.front=front->next B.s->next=rear;rear=s C.rear->next=s;rear=s; D.s->next=front;front=s;
A.S->top==0 B.S->top!=0 C.S->top==n D.S->top!=n