A.rear->next=p;rear=p; B.rear->next=p;p=rear; C.p=rear->next;rear=p; D.rear=p;rear->next=p;
A.3,2,4,1 B.3,2,1,4 C.4,3,2,1 D.1,4,2,3
A.n/2 B.n C.n-1 D.1