问题 单项选择题

对如下二叉树,进行后序遍历的结果为【 】

A.ABCDEF

B.DBEAFC

C.ABDECF

D.DEBFCA

答案

参考答案:D

解析:二叉树后序遍历的简单描述如下:若二叉树为空,则结束返回。否则(1)后序遍历左子树:(2)后序遍历右子树;(3)访问根结点。也就是说,后序遍历是指在访问根结点、遍历左子树与遍历右子树这三者中,首先遍历左子树,然后遍历右子树,最后访问根结点,并且在遍历左、右子树时,仍然先遍历左子树,然后遍历右子树,最后访问根结点。根据后序遍历的算法,后序遍历的结果为DEBFCA。

阅读理解

A group of swans flew down to a beach where a crow (乌鸦) was jumping around. The crow watched them with disdain (笔试).

“You have no flying skills at all!” he said to the swans. “All you can do is to move your wings. Can you turn over in the air? No, that’s beyond you. Let’s have a flying competition. I’ll show you what real flying is!”

One of the swans, a strong young male, took up the challenge (挑战). The crow flew up and began to show his skills. He flew in circles, performed other flying tricks, and then came down and looked proudly at the swan.

Now it was the swan’s turn. He flew up, and began flying over the sea. The crow flew after him, making all kinds of comments (评价) about his flying. They flew on and on till they couldn’t see the land and there was nothing but water on all sides. The crow was making fewer and fewer comments. He was now so exhausted that he found it hard to stay in the air, and had to struggle to keep himself from falling into the water.

The swan pretended (假装) not to notice, and said, “Why do you keep touching the water, brother? Is that another trick? “

“No,” said the crow. He knew he had lost the competition. “I’m in trouble because of my pride (自大) ! If you don’t help me, I’ll lose my life...”

The swan took pity on him, and took him on his shoulders and flew back to the beach.

小题1:What’s the correct order of the following events?

a. The crow followed the swan and got into trouble.

b. The swan felt pity for the crow and saved it.

c. The crow had to ask the swan for help.

d. The swan accepted a challenge of performing flying tricks.

A.a, d, b, c

B.a, b, d, c

C.d, a, c, b

D.d, c, a, b小题2:What does the underlined word “exhausted” in Paragraph 4 mean?

A.Tired.

B.Bored.

C.Nervous.

D.Frightened.小题3:What do we learn from the passage?

A.Practice makes perfect.

B.The early bird catches the worm.

C.No pains, no gains.

D.Pride goes before a fall.

选择题