postorder for binary tree

例句：

1. 1. The postorderof the tree is crucial for its survival.
   树木的后序对于其生存至关重要。
2. 2. Thepostorder of the data is important foranalysis.
   数据的顺序对于分析很重要。
3. 3. The postorderof the task is to complete it first.
   任务的后序是先完成它。