有下列二叉树，对此二叉树前序遍历的结果是（）。 A．ACFXDBEYZ_爱下问搜题

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问题单项选择题

有下列二叉树，对此二叉树前序遍历的结果是（）。

A．ACFXDBEYZ

B．ABEFXYZCD

C．ABCDEFXYZ

D．ABDYECFXZ

答案

参考答案：D

解析：

对二叉树的前序遍历是指：先访问根结点，然后访问左子树，最后访问右子树，并且，在访问左、右子树时，先访问根结点，再依次访问其左、右于树。记住3种遍历的顺序：(1) 前序，访问根一按前序遍历左子树一按前序遍历右子树；(2) 中序，按中序遍历左子树一访问根一按中序遍历右子树：(3) 后序，按后序遍历左子树一按后序遍历右子树一访问根。

完形填空

I sat with my friend in a well-known coffee shop in a neighboring town of Venice. As we        our coffee, a man came in and sat at a(n)        table beside us. He called the waiter and placed his        saying, “Two cups of coffee, one of them there on the wall”. We        this order with rather interest and observed that he was        with one cup of coffee but he paid for two. As soon as he left, the waiter         a piece of paper on the wall saying “A Cup of Coffee”.
While we were still there, two other men        and ordered three cups of coffee, two on the table and one on the wall. They had two cups of coffee but        for three and left. This time also, the        did the same; he put up a piece of paper on the wall saying, “A cup of coffee.” It seemed that this gesture was a        at this place.        , it was something unique and puzzling for us. Since we had         to do with the matter, we        our coffee, paid the bill and left.
After a few days, we again had a(n)        to go to this coffee shop. While we were enjoying our coffee, a man walked in. The way this man was dressed did not        the standard nor the atmosphere of this coffee shop. Poverty was       from the looks on his face.        he seated himself, he looked at the wall and said, “One cup of coffee from the         .” The waiter served coffee to this man with        and dignity. The man had his coffee and left without paying. We were amazed to watch all this when the waiter        a piece of paper from the wall and threw it into the dustbin.

A．carelessness

A．brought down

单项选择题

被称为“音乐之都”的城市是（）

A.巴黎

B.伦敦

C.罗马

D.维也纳