问题 单项选择题

全球多媒体网络的研究领域是安全性,下列描述错误的是______。

A.用户可能需要屏蔽通信量模式

B.加密可能会妨碍协议转换

C.网络是共享资源,但用户的隐私应该加以保护

D.加密地点的选择无关紧要

答案

参考答案:D

解析:网络是共享资源,它为广大用户和服务团体提供了访问优势,也带来了严重违背安全性、缺乏隐私 和易被攻击的缺点。在一些情况下,用户希望掩饰他们之间正在发生通信的事实,这就需要屏蔽通信量模 式,防止入侵者通过对通信量的观察,造成称为通信量分析的网络安全威胁。加密隐藏了比特流基本的语 法和语义元素,因此妨碍了很多重要的处理,如协议转换、信源/信道联合编码等。在网络体系结构中,重要的问题是选择合适的加密地点。在低层(如网络层或数据链路层)开展加密,能够加密路由信息,而高层无法知晓,这可以更好地屏蔽通信量模式。然而,在网间网关上,如 OSI 和 TCP/IP 之间,用户数据将不得不解密和重新加密,使得窃听变的容易。在高层(如应用层)上展开加密,虽有用 户数据可端—端加密的优势,但是由低层上附加上的标头却没有加密,这暗示了通信量模式,使入侵者有 机可乘。另外,高层加密需要加密的实体数非常巨大,因为与应用相关的每一个用户进程都需加密。

阅读理解

B

Taste is such a subjective matter that we don’t usually conduct preference tests for food.The most you can say about anyone’s preference is that it’s one person’s opinion.But because the two big cola companies-Coca-Cola and Pepsi Cola-are marketed so aggressively, we’ve wondered how big a role taste preference actually plays in brand loyalty.We set up a taste test that challenged people who identified themselves as either Coca-cola or Pepsi fans: Find your brand in a blind tasting.

We invited staff volunteers who had a strong liking for either Coca-Cola Classic or Pepsi, Diet Coke, or Diet Pepsi.These were people who thought they’d have no trouble telling their brand from the other brand.

We eventually located 19 regular cola drinkers and 27 diet cola drinkers.Then we fed them with four unidentified samples of cola one at a time, regular colas for the one group, diet versions for the other.We asked them to tell us whether each sample was Coke or Pepsi; then we analyzed the records statistically to compare the participants’ choices with what mere guesswork could have accomplished.

Getting all four samples right was a tough test, but not too tough, we thought, for people who believed they could recognize their brand.In the end, only 7 out of 19 regular cola drinkers correctly identified their brand of choice in all four trials.The diet-cola drinkers did a little worse-only 7 out of 27 identified all four samples correctly.

Both groups did better than chance would predict, but nearly half the participants in each group made the wrong choice two or more times.Two people got all four samples wrong.Overall, half the participants did about as well on the last round of tasting as on the first, so tiredness, or taste burnout, was not a factor.Our preference test results suggest that only a few Pepsi participants and Coke fans may really be able to tell their favorite brand by taste and price.

41.According to the passage the preference test was conducted in order to ________.

A.show that a person’s opinion about taste is mere guesswork

B.compare the ability of the participants in choosing their drinks

C.find out the role taste preference plays in a person’s drinking

D.reveal which cola is more to the liking of the drinkers

42.The statistics recorded in the preference tests show that________.

A.there is not much difference in taste between Coca-Cola and Pepsi

B.few people had trouble telling Coca-Cola from Pepsi

C.people’s tastes differ from one another

D.Coca-Cola and Pepsi are people’s two most favorite drinks

43.It is implied in the first paragraph that________.

A.the competition between the two colas is very strong

B.blind tasting is necessary for identifying fans

C.the purpose of taste test is to promote the sale of colas

D.the improvement of quality is the chief concern of the two cola companies

44.The underlined word “burnout” here refers to the state of________.

A.being seriously burnt in the skin           

B.being badly damaged by fire  

C.being unable to burn for lack of fuel     

D.being unable to function because of too much use

45.The author’s purpose in writing this passage is to________.

A.emphasize that taste and price are closely related to each other

B.recommend that blind tasting be introduced in the quality control of colas

C.show that taste preference is highly subjective

D.argue that taste testing is an important marketing strategy

单项选择题