19. 將下列 10 個數:15,5,20,35,10,30,8,18,25,12 依序建成二元搜尋樹後，以後序法（postorder）追蹤之結果為何？
(A)8,10,12,5,18,25,30,35,20,15
(B)8,12,10,5,18,25,30,35,20,15
(C)8,12,10,5,18,25,35,30,25,15
(D)5,8,10,12,15,18,20,25,30,35