己知P 结点是某双向链表的中间结点,试从下列提供的答案中选择合适的语句序列。 a. 在P 结点后插入S 结点的语句序列是 _____ b. 在P 结点前插入S 结点的语句序列是 _____ c. 删除P 结点的直接后继结点的语句序列是 _____ d. 删除P 结点的直接前驱结点的语句序列是 _____ e. 删除P 结点的语句序列是 _____ (l) P — >next =P — >next — > next ; (2) p — >prev =P — > prev — > prev ; (3) p — >next = S; (4) p — > prev =S; (5) S — >next = P; (6) S — > prev =P; (7) S — >next = P — >next ; (8) S — > prev =P — > prev ; (9) P — > prev — > next = P — > next ; (10) p — > prev — > next = P; (11) p — > next — > prev = P ; (12) P — > next — > prev =S; (13) P — > prev — > next = S; (14) p — >next — > prev = P — > prev ; (15) Q =P — > next ; (16) Q =P — > prev ; (l7) delete P ; (18) delete Q ;