二叉搜索树的前序遍历由 12, 8, 6, 2, 7, 9, 10, 16, 15, 19, 17, 20 给出。
那么这棵树的后序遍历是：
(一) 2, 6, 7, 8, 9, 10, 12, 15, 16, 17, 19, 20
(乙) 2, 7, 6, 10, 9, 8, 15, 17, 20, 19, 16, 12
(C) 7, 2, 6, 8, 9, 10, 20, 17, 19, 15, 16, 12
(四) 7, 6, 2, 10, 9, 8, 15, 16, 17, 20, 19, 12答案：(乙)
解释：从前序画二叉搜索树，然后写后序。
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