单项选择题
A.q->prior =p；p->next=q；p ->next ->prior =q；q ->next =p ->next；
B.q ->next =p ->next；p ->next ->prior =q；p->next=q；q->prior =p；
C.p->next=q；q->prior =p；q ->next =p ->next；p ->next ->prior =q；
D.p ->next ->prior =q；q->prior =p；p->next=q；q ->next =p ->next；