单选题While hackers with motives make headlines, they represent less than 20% of all net- work security breaches. More common are instances of authorized users accidentally winding 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 department 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 machines 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 performance. 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 protocols and applications, and they require no changes in client applications, no specific application 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 addition, they lack audit mechanisms. Some packet filters are implemented inside routers, limiting computing power and filtering capabilities. Others are implemented as s9ftware 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.

单选题Although at the______these schools were attended by only a tiny percentage of the population, numbers increased during the 19 th century as waves of immigrants entered.

单选题Australia is struggling to cope with the consequences of a devastating drought. As the world warms up, other countries should pay______ A. heel B. heal C. heed D. head

单选题The teacher's role is not simply to______knowledge to students; he should also set a good example for them.

单选题Under ethical guideline recently adopted by the National Institutes of Health, human genes are to be manipulated only to correct disease for which ______ treatments are unsatisfactory.

单选题We do not mean to be disrespectful when we refuse to follow the advice of our leader.

单选题Compared mathematically to smoking and driving, almost everything else seems relatively risk-free, ______ almost nothing seems worth regulation.

单选题The sheer diversity of tropical plants represents a seemingly ______ source of raw materials, of which only a few have been utilized.

单选题Today, the computer has taken up appliance status in more than 42 percent of households across the United States. And these computers are increasingly biting wired to the Internet. Online access was up more than 50 percent in just the past year. Now, more than one quarter of all U.S. households can surf in cyberspace. Mostly, this explosive growth has occurred democratically. The online penetration and computer ownership increases extend across all the demographic levels — by race, geography, income, and education. We view these trends as favorable without the slightest question because we clearly see computer technology as empowering. In fact, personal growth and a prosperous U.S. economy are considered to be the long-range rewards of individual and collective technological power. Now for the not-so-good news. The government's analysis spells out so-called digital divide. That is, the digital explosion is not booming at the same pace for everyone. Yes, it is true that we are all plugged in to a much greater degree than any of us have been in the past. But some of us are more plugged in than others and are getting plugged in far more rapidly. And this gap is widening even as the pace of the information age accelerates through society. Computer ownership and Internet access are highly classified along lines of wealth, race, education, and geography. The data indicates that computer ownership and online access are growing more rapidly among the most prosperous and well educated: essentially, wealthy white people with high school and college diplomas and who are part of stable, two-parent households. The highest income bracket households, those earning more than $ 75,000 annually, are 20 times as likely to have access to the Internet as households at the lowest income levels, under $10,000 annually. The computer-penetration rate at the high-income level is an amazing 76.56 percent, compared with 8 percent at the bottom end of the scale. Technology access differs widely by educational level. College graduates are 16 times as likely to be Internet surfers at home as are those with only elementary-school education. If you look at the differences between these groups in rural areas, the gap widens to a twenty-six-fold advantage for the college-educated. From the time of the last study, the information-access gap grew by 29 percent between the highest and lowest income groups, and by 25 percent between the highest and lowest education levels. In the long run, participation in the information age may not be a zero sum game, where if some groups win, others must lose. Eventually, as the technology matures we are likely to see penetration levels approach all groups equally. This was true for telephone access and television ownership, but eventually can be cold comfort in an era when tomorrow is rapidly different from today and unrecognizable compared with yesterday.

单选题Machiavelli cautions the prince not to Urelinquish/U power under passing duress.

单选题The consumer ______ in recent years has led to an explosion of shopping center development in big cities like Beijing, Shanghai and Canton. A. boom B. volume C. summit D. pressure

单选题By education, I mean the influence of the environment upon the individual to produce a permanent change in the habits of behavior, of thought and of attitude．It is in being thus susceptible to the environment that man differs from the animals, and the higher animals from the lower．The lower animals are influenced by the environment but not in the direction of changing their habits．Their instinctive responses are few and fixed by heredity．When transferred to an unnatural situation, such an animal is led astray by its instincts．Thus the "ant-lion"whose instinct implies it to bore into loose sand by pushing backwards with abdomen, goes backwards on a plate of glass as soon as danger threatens, and endeavors, with the utmost exertions to bore into it．It knows no other mode of flight, "or if such a lonely animal is engaged upon a chain of actions and is interrupted, it either goes on vainly with the remaining actions(as useless as cultivating an unsown field)or dies in helpless inactivity"． Thus a net-making spider which digs a burrow and rims it with a bastion of gravel and bits of wood, when removed from a half finished home, will not begin again, though it will continue another burrow, even one made with a pencil． Advance in the scale of evolution along such lines as these could only be made by the emergence of creatures with more and more complicated instincts．Such beings we know in the ants and spiders．But another line of advance was destined to open out a much more far-reaching possibility of which we do not see the end perhaps even in man．Habits, instead of being born ready-made(when they are called instincts and not habits at all), were left more and more to the formative influence of the environment, of which the most important factor was the parent who nOW cared for the young animal during a period of infancy in which vaguer instincts than those of the insects were molded to suit surroundings which might be considerably changed without harm． This means, one might at first imagine, that gradually heredity becomes less and environment more important．But this is hardly the truth and certainly not the whole truth．For although fixed automatic responses like those of the insect-like creatures are no longer inherited, although selection for purification of that sort is no longer going on, yet selection for educability is very definitely still of importance．The ability to acquire habits can be conceivably inherited just as much as can definite responses to narrow situations．Besides, since a mechanism--is now,for the first time, created by which the individual(in contradiction to the species)can be fitted to the environment, the latter becomes, in another sense, less not more important．And finally,less not the higher animals who possess the power of changing their environment by engineering feats and the like, a power possessed to some extent even by the beaver,and preeminently by man．Environment and heredity are in no case exclusive but always—supplementary factors．

单选题The ______ of the occasion was spoiled when she fell down the steps. A. privacy B. dignity C. morality D. secrecy

单选题I shall tell him the truth, ______.

单选题The mother was_____with grief when she heard that her child was dead.

单选题Although crowded cities seem to be a ______ of our crowded world, only 10 percent of the world' s people live in cities as large as Madrid or larger.