问题 单项选择题

按照"后进先出"原则组织数据的数据结构是【 】

A.队列

B.栈

C.双向链表

D.二叉树

答案

参考答案:B

解析:"后进先出"表示最后被插入的元素最先能被删除。选项A中,队列是指允许在一端进行插入、而在另一端进行删除的线性表,在队列这种数据结构中,最先插入的元素将最先能够被删除,反之,最后插入的元素将最后才能被删除,队列又称为"先进先出"的线性表,它体现了"先来先服务"的原则;选项B中,栈顶元素总是最后被插入的元素,从而也是最先能被删除的元素,栈底元素总是最先被插入的元素,从而也是最后才能被删除的元素。队列和栈都属于线性表,它们具有顺序存储的特点,所以才有"先进先出"和"后进先出"的数据组织方式。双向链表使用链式存储方式,二叉树也通常采用链式存储方式,它们的存储数据的空间可以是不连续的,各个数据结点的存储顺序与数据元素之间的逻辑关系可以不一致。所以选项C和选项D错误。

阅读理解

Today’s generation of young people is the largest in human history. Nearly half the world’s population — more than 3 billion people — are under the age of 25. More than half the world’s young people — about 850 million between the ages of 10 and 24 — live in Asia and the Pacific region.

This rapidly expanding youth population is increasingly vulnerable to HIV.  Young people are at the center of the HIV/AIDS epidemic . Of the 10 million young people living with HIV worldwide, 21% live in Asia and the Pacific region. When surveying of all new HIV/AIDS cases globally, nearly a quarter of all people living with HIV/AIDS are under the age of 25. An estimated 6,000 young people are infected every day — one every 14 minutes. The majority are women and girls. In South Asia, where over 1 million young people between the ages of 15 to 24 are infected with HIV, more than half (62%) are young women.

Young people are key to defeating the HIV/AIDS epidemic. Yet in most countries, they lack the information, education and services that will enable them to make informed and healthy choices about their health, and the needs of youths are often ignored. UNESCO, in collaboration with other UN agencies, governments, NGOs and community-based organizations, makes efforts to ensure the health needs of youths, including HIV prevention education, programs and policies implemented throughout Asia and the Pacific region.

59. How many young people with HIV live in Asia and the Pacific area?

A. 3 billion               B. 850 million        C. 100 million           D. 2.1 million

60. Which of the following statements is NOT true?

A. It’s young people themselves that can defeat HIV.

B. Most cases infected with HIV are young people.

C. Most young people who are infected with HIV are women.

D. Half of the world population is infected with HIV.

61. From the passage we can conclude that ________.

A. more and more young people will be infected with HIV

B. it’s because of not being informed that young people are easy to be infected

C. people in Asia and the Pacific region are easy to be infected

D. there is no policy for teenagers’ prevention of HIV

单项选择题