问题 单项选择题

下面关于完全二叉树的叙述中,错误的是 ______。

A.除了最后一层外,每一层上的结点数均达到最大值

B.可能缺少若干个左右叶子结点

C.完全二叉树一般不是满二叉树

D.具有结点的完全二叉树的深度为[log2n]+1

答案

参考答案:B

解析:[评析] 这里考察完全二叉树与满二叉树的定义及二叉树的性质。满二叉树指除最后一层外每一层上所有结点都有两个子结点的二叉树。完全二叉树指除最后一层外,每一层上的结点数均达到最大值,在最后一层上只缺少右边的若干子结点(叶子结点)的二叉树。因此选项A是正确的,而选项B是错误的。由定义可知,满二叉树肯定是完全二叉树,而完全二叉树一般不是满二叉树,因此选项C是正确的叙述。选项D即二叉树性质(5),也是正确的。

阅读理解

Dear Reader,

Think about an 11-year-old child spending her days washing clothes, looking after a baby brother, and doing hard work on the farm.

Think about a little girl. She knows there will not be enough food for dinner, and has no water to drink because it is not clean. She has watched her father, brother and sister lose their lives as the family has no money to send for a doctor.

Hard to believe? For Maria Pastora, these are the facts of life.

Maria would gladly walk to school, but her mother, now alone, really needs her at home. Maria had to leave school to work for her poor family.

But for five dollars a week, you can help out a child like Maria. Show her that somewhere, some­one will help her. Through Save the Children, you can help Maria’s mother get better crops (收成) from their farm, and earn the money to buy clothes and things for school.

To help Maria most, your money is to put to­gether with other helpers, so hardworking people can help themselves. Build a school or a hospital, make their farm better, bring in clean water... This is what Save the Children has been about since 1932.

For you there are many returns. You can write letters to each other, get photos, or study reports. Know you are helping and saving another person in the same world as you. That’s how Save the Chil­dren works. But without you, it can’t work. Please take a moment to fill in this form to help a child like Maria and her village.

It can make such a difference in her life and yours.

Save the Children

David L. Guyer

Chairman

(    ) 7. Maria’s father, brother and sister died because they_________.

A. were too poor to see a doctor   B. didn’t know where to find a doctor

C. didn’t have enough food to eat  D. were too busy to see a doctor

(    ) 8. This letter mainly tells you to_________.

A. know about poor people   B. earn some money for poor children

C. show pity to poor people   D. donate money to help poor children

(    ) 9. If you try to help a child like Maria, which of the following can’t you get from her?

A. You can often get some pictures from her.

B. You can get more money from her when she grows up.

C. You can often get her letters.

D. You can often be told how she is getting on.

(    ) 10. This letter most probably appears_________.

A. on TV     B. in a magazine     C. in a dictionary    D. on the radio

多项选择题