在双向指针p的结点前插入一个指针q的结点操作是( )
A.
p->prior=q; q->next=p; p->prior->next=q; q->prior=q;
B.
p->prior=q; p->prior->next=q; q->next=p; q->prior=p->prior;
C.
q->prior=p->prior; q->next=p; p->prior->next=q; p->prior=q;
D.
q->prior=p->prior; q->next=q; p->prior=q; p->prior=q;