[单项选择]在一个双链表中,在*P结点之前插入*q结点的操作是( )。 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;q->prior->next=q;q->next=P; D. p->prior->next=q;q->next=P;q->prior=p->prior;p->prior=q;