| 考博易错题（2019/6/14） |
| 第1题： 2 While hackers with motives make headlines, they represent less than 200% of all net work security breaches. More common are instances of authorized users accidentally wind ing up where they should not be and inadvertently deleting or changing datA、However, the Internet introduces another concern: some Internet surfers are bound to go where they have no business and, in so doing, threaten to wipe out data to which they should not have access. Before picking a firewall, companies need to adopt security policies.A、security policy states who or what is allowed to connect to whom or what. You can group all users by de partment or classification. The better firewall products let you drag and drop groups in a graphical user interface (GUI) environment to define network security easily. Two methods are most often used together to establish an Internet firewall. They are application and circuit gateways, as well as packet filtering. With application and circuit gateways, all packets are addressed to a user-level application on a gate-way that relays packets between two points. With most application gateways, additional packet-filter ma chines are required to control and screen traffic between the gateway and the networks.A" typical configuration includes two routers. With a bastion host that serves as the application gateway sitting between them. A、drawback to application and circuit gateways is that they slow network perform- ance. This is because each packet must be copied and processed at least twice by all the communication layers. Packet-filter gateways, which act as routers between two nets, are less secure than application gateways but more efficient. They are transparent to many pro tocols and applications, and they require no changes in client applications, no specific ap plication management or installation, and no extra hardware. Using a single, unified packet-filter engine, all net traffic is processed and then for warded or blocked from a single point of control. However, most packet filters are state less, understand only low-level protocols, and are difficult to configure and verity. In ad dition, they lack audit mechanisms. Some packet filters are implemented inside routers, limiting computing power and filtering capabilities. Others are implemented as software packages that filter the packets in application-layer processes, an inefficient approach that requires multiple data copies, expensive delays and context switches and delivers lower throughput. So what’s a network administrator to do Some vendors are developing firewalls that overcome many of these problems and combine the advantages of application gateways and packet filtering. These efficient, protocol-independent, secure firewall engines are capable of application-level security, user authentication, unified support, and handling of all protocols, auditing and altering. They are transparent to users and to system setup, and include a GUI for simple and flexible system management and configuration. For whom is this passage most likely writtenA．Government officials. B．Hackers. C．Network administrators. D．Computer experts. |
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| 第2题：Like many other aspects of the computer age, Yahoo began as an idea, (21) into a hobby and lately has (22) into a full-time passion. The two developers of Yahoo,David Filo and Jerry Yang, Ph.D、candidates (23) ElectricalEngineering at Stanford University, started their guide inApril 1994 as a way to keep (24) of their personal interest on the Internet.Before long they (25) that their homebrewed lists were becoming too long and (26) . Gradually they began to spend more and more time on Yahoo. During 1994, they (27) yahoo into a customized database designed to (28) the needs of the thousands of users (29) began to use the service through the closely (30) Internet community. They developed customized software to help them (31) locate, identify and edit material (32) on the Internet. The name Yahoo is (33) to stand for "YetAnother Hierarchical Officious Oracle", but Filo and Yang insist they selected the (34) because they considered themselves yahoos. Yahoo itself first (35) on Yang’s workstation, "akebono", while the search engine was (36) on Filo’s computer, "Konishiki" . In early 1995 MarcAndersen, co-founder of NetscapeCommunication in Mountain View,California, invited Filo and Yang to move their files (37) to larger computers (38) at Netscape.As a result Stanford’s computer network returned to (39) , and both parties benefiteD、Today, Yahoo (40) organized information on tens of thousands of computers linked to the weB、 A、over B、away C、insideD、beneath |
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| 第3题：What are the chances that we will encounter some alien form of life, as we explore the galaxy. If the argument about the time scale for the appearance of life onEarth is correct, there ought to be many other stars, whose planets have life on them. Some of these stellar systems could have formed 5 billion years before theEarth. So why is the galaxy not crawling with self designing mechanical or biological life forms Why hasn’t theEarth been visited, and even colonizeD、I discount suggestions that UFOs contain beings from outer space. I think any visits by aliens would be much more obvious, and probably also, much more unpleasant. What is the explanation of why we have not been visited One possibility is that the argument about the appearance of life onEarth is wrong. Maybe the probability of life spontaneously appearing is so low thatEarth is the only planet in the galaxy, or in the observable universe, in which it happeneD、 Another possibility is that there was a reasonable probability of forming self-reproducing system, like cells, but most of these forms of life did not evolve intelligence. A、third possibility is that there is a reasonable probability for life to form, and to evolve to intelligent beings, in the external transmission phase.But at that point, the system becomes unstable, and the intelligent life destroys itself. This would be a very pessimistic conclusion. I very much hope it isn’t true. I prefer a fourth possibility: there are other forms of intelligent life out there, but we have been overlookeD、There used to be a project called SETI, the search for extraterrestrial intelligence. It involved scanning the radio frequencies, to see if we could pick up signals from alien civilizations. I thought this project was worth supporting, though it was cancelled due to a lack of funds.But we should have been wary of answering back, until we have developed a bit further. Meeting a more advanced civilization, at our present stage, might be a bit like the original inhabitants ofAmerica meetingColumbus. I don’t think they were better off for it. By comparison, the author considers that ______. A、a more advanced civilization will destroy us if they visit us at present B、the original inhabitants ofAmerica were better off because ofColumbus’ visit C、being visited by a more advanced civilization will do us good D、we wouldn’ t be better off even though we were visited by the beings from outer space at present |
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| 第4题： Although it was his first experience as chairman, he ______ over the meeting with great skill. A．presided B．administered C．mastered D．executed |
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| 第5题： The primary purpose of paragraph I is to ______. A．summarize past research and introduce a new study B．describe a historical period C．emphasize the advantages of one theory over another D．define a term and illustrate it with an example |
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