A.p->next=s;s->prior=p;p->next->prior=s;s->next=p->next; B.p->next=s;p->next->prior=s;s->prior=p;s->next=p->next; C.s->prior=p;s->next=p->next;p->next=s;p->next->prior=s; D.s->prior=p;s->next=p->next;p->next->prior=s;p->next=s
A.s->next=p->next;p->next=s; B.q->next=s;s->next=p; C.p->next=s->next;s->next=p; D.p->next=s;s->next=q;