A.使结点P指向结点q,再使结点q指向结点P的后件结点B.使结点q指向P的后件结点,再使结点P指向结点qC.使结点q指向结点P,再使结点P指向结点q的后件结点D.使结点P指向q的后件结点,再使结点q指向结点P