在双链表中向p所指的结点之前插入一个结点q的操作为().
A. p->prior=q; q->next=p;p->prior->next=q;q->prior=p->prior;
B. q->prior=p->prior;p->prior->next=q; q->next=p;p->prior=q->next;
C. q->next=p;p->next=q;4->prior->next=q;q->next=p;
D. p->prior->next=q; q->next=p;q->prior=p->prior;p->prior=q;