问题 单项选择题

若文件系统容许不同用户的文件可以具有相同的文件名,则操作系统应采用()来实现。

A.索引表

B.索引文件

C.指针

D.多级目录

答案

参考答案:D

解析:

[分析]: 本题考查的是操作系统中文件管理的基本知识及应用。常见的目录结构有三种:一级目录结构、二级目录结构和多级目录结构。一级目录的整个目录组织是一个线性结构,在整个系统中只需建立一张目录表,系统为每个文件分配一个目录项(文件控制块)。一级目录结构简单,但缺点是查找速度慢,不允许重名和不便于实现文件共享等,因此它主要用在单用户环境中。为了克服一级目录结构存在的缺点,引入了二级目录结构。二级目录结构是由主文件目录MFD(Master File Directory)和用户目录UFD(User File Directory)组成的。采用二级目录结构也存在一些问题。该结构虽然能有效地将多个用户隔离开,这种隔离在各个用户之间完全无关时是一个优点;但当多个用户之间要相互合作去共同完成一个大任务,且一个用户又需去访问其他用户的文件时,这种隔离便成为一个缺点,因为这种隔离使诸用户之间不便于共享文件。所以引入多级目录结构,这样允许不同用户的文件可以具有相同的文件名。

单项选择题 B型题
填空题

Part 4


Questions 26-45


·Read the following passage and decide which answer best fits each space.
·For questions 26-45, mark one letter A, B, C or D on the Answer Sheet.
Participation (26) high school sports is not a constitutional right. (27) , it is a privilege, paid for by taxpayers, open to students who promise to (28) certain conduct requirements on and off the field. One of these promises is to (29) from using drugs. Drug use is a serious problem among high school students. Studies show that as many as 500, 000 high school students use muscle-pumping, life-destroying substances such as steroids. Many more use illegal drugs, (30) cause discipline problems and (31) the stage for lifelong (32) .
Drug testing works to (33) and identify use. That is why drug testing is required to compete in the Olympics, the National Collegiate Athletic Association and the National Football League. (34) drug testing was instituted by these organizations, use of performance- (35) drugs has been greatly reduced. We should want (36) in schools.
Indeed, many athletes (37) testing programs, and no wonder. Without testing, athletes have to choose between drug use and a competitive disadvantage (38) the field.
Those who challenge the need for drug testing may be forgetting (39) it is like be an adolescent. Peer pressure is enormous, and one of the few effective counter-weights is the fear of being caught. More importantly, once drug use is (40) , a school can (41) to the student before he or she gets addicted or arrested.
For 25 years, public schools (42) by federal judges and civil libertarians, with results everyone can see. It is time (43) decisions on how to run public schools locally (44) officials. There is nothing unconstitutional about asking those who gain the advantages of school-sponsored athletics to contribute to the safety of other players, the integrity of the game and their own well-being. The Supreme Court should leave these programs (45) .

A.identified

B.recognized

C.discern

D.research