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针对用户的需求，设计师提出了用物理隔离来实现网络安全的方案。经过比较，决定采用隔离网闸实现物理隔离。物理隔离的思想是 7 ，隔离网闸的主要实现技术不包括 8 。 可以把所有使用DHCP协议获取IP地址的主机划分为不同的类别进行管理。下面的选项列出了划分类别的原则，其中合理的是 。
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Our ape-men forefathers had no obvious natural weapons in the struggle for【1】in the open. They had neither the powerful teeth nor the strong claws of the big cats. They could not【2】with the bear, whose strength, speed and claws【3】an impressive " small fire" weaponry. They could not even defend themselves【4】running swiftly like the horses, zebras or small animals. If the ape-men had attempted to compete on those terms in the open, they would have been【5】to failure and extinction. But they were【6】with enormous concealed advantages of a kind not possessed by any of their competitors. In the search【7】the pickings of the forest, the ape-men had【8】efficient stereoscopic vision and a sense of color that the animals of the grasslands did not【9】. The ability to see clearly at close range permitted the ape-men to study practical problems in a way that lay far【10】the reach of the original inhabitants of the grassland. Good long-distance sight was【11】another matter. Lack of long-distance vision had not been a problem for forest-dwelling apes and monkeys because the【12】the viewpoint, the greater the range of sight-so【13】they had had to do was climb a tree. Out in the open, however, this simple solution was not【14】. Climbing a hill would have helped, but in many places the ground was flat. The ape-men【15】the only possible solution. They reared up as high as possible on their hind limbs and began to walk【16】. This vital change of physical position brought about considerable disadvantages. It was extremely unstable and it meant that the already slow ape-men became【17】still.【18】, they persevered and their bone structure gradually became【19】to the new, unstable position that【20】them the name Homo erectus, upright man.
In the 1960s, Peru"s sugar industry was among the most efficient in the world. It was all downhill thereafter. A military government expropriated the sugar estates on the country" s north coast, turning them into government-owned co-operatives. Having peaked at 1m tonnes in 1975, output fell to 400,000 tonnes by the early 1990s. But since then the sugar industry has passed into private hands again. Over the past decade production has returned to its historic peak—and is now set to boom. The change has been gradual. The government has sold its stake in the industry in tranches. But now investors are piling in. As in other parts of South and Central America they are attracted by higher prices for sugar because of its use for ethanol. Industry sources predict that land under sugar will expand by 10,000 hectares (25,000 acres) a year, more than doubling output over the next decade. That would turn Peru into an exporter—though not on the scale of Brazil or Colombia. Last year, local investors secured a controlling stake in Casa Grande, the largest sugar plantation. Bioterra, a Spanish company, plans a $ 90m ethanol plant nearby. Maple, a Texas company, has bought 10,600 hectares of land in the northern department of Piura. Its plans call for an investment of $120m and ethanol production of 120m litres a year. Brazilian and Ecuadorean investors are also active. Part of the attraction is that Peru has signed a free-trade agreement with the United States. Provided that it can satisfy the concerns of the new Democratic-controlled Congress in Washington D. C., about the enforcement of labour rights, this agreement should be approved later this year. It would render permanent existing trade preferences under which ethanol from Peru can enter the United States dutyfree. By contrast, ethanol exported from Brazil, the world"s biggest producer, must pay a tariff of 54 cents a gallon. Two harsh realities might sour these sweet dreams. Colombia, Central America and the Dominican Republic all enjoy similar preferences and have similar plans. Colombia already produces 360m litres a year of ethanol, much of it for export. The second question is whether sugar—a thirsty crop—is the best use of Peru"s desert coastal strip, with its precarious water supply. One of the country"s achievements of the past decade has been the private sector"s development of new export crops. It would be ironic if these businesses were threatened by sugar"s privatisation. Which of the following is the best title for this text
Jim Boon is a hybrid kind of guy. He drives a Toyota hybrid to work, a Honda hybrid on weekends and, as a manager for Seattle public transit he recently placed the world"s largest order for hybrid electric buses. Now, with the biggest hybrid-bus fleet in the world, Seattle has become the main testing ground for a technology that claims it can drastically cut air pollution and fuel consumption. In the 1990s, demo fleets of 35 buses or fewer started cropping up in cities such as Tempe, Ariz. Sixteen of these early hybrids still service Genoa, Italy, where drivers switch from diesel to electric power when passing the city"s downtown architectural treasures. But no city has gone as far as Seattle, which last year bought 235 GM hybrid buses at $ 645,000 a pop. When the final one rolls out this December, the region"s bus system will be 15 percent hybrid. But why Seattle, and why now The Pacific Northwest has long been a hotbed of both Green politics and cutting-edge technology. Fourteen years ago the Seattle area bought 236 Italian-made Breda buses to service a mile-long downtown tunnel. They were supposed to operate as clean electric trolleys underground, but the switching mechanism often failed and "the bus drove through the tunnel as a diesel," says Boon. "It was pretty loud and smoky. " When the Bredas hit retirement age in 2002, Boon went shopping. He chose the GM buses because they use an automatic transmission and diesel boosters that provide power to scale inclines without strain. In hilly Seattle, the prospect of a hybrid that could climb like a diesel but accelerate without belching black fumes helped justify a price $ 200,000 higher than that of a regular bus. "The days of seeing a diesel pull away and pour out smoke are over," says Boon. "After we drove these hybrid buses across the country, I wiped a handkerchief inside the tailpipe. It came out spotless. " Experts say buses are critical to realizing the hybrid dream of greater efficiency and cleaner air. It would take thousands of hybrid cars to save as many gallons of gas (750,000) as Boon expects his buses to save Seattle each year. GM claims that compared with conventional diesels, its new buses also churn out 90 percent less particulate matter—a known carcinogen. "Buses are a major source of pollution in any city," says Dave Kircher of the Puget Sound Clean Air Agency. "They operate where people are breathing this exhaust, so this is a major step forward in terms of emissions. " And a major step forward in the marketplace: Philadelphia, Honolulu, Long Beach, Calif., and Albuquerque, N. M. , have all bought the GM buses in recent months. GM is now touting itself in ads as the top hybrid-bus innovator, but Siemens is among the global giants dueling GM for new business, and New York plans to deploy 325 BAE Systems hybrids by 2006. "There"s room for competition," says James Cannon, editor of Hybrid Vehicles newsletter. Seems Seattle isn"t the only city trying to leave grunge behind. Why are buses critical to realizing the hybrid dream of higher efficiency
In the 1960s, Peru"s sugar industry was among the most efficient in the world. It was all downhill thereafter. A military government expropriated the sugar estates on the country" s north coast, turning them into government-owned co-operatives. Having peaked at 1m tonnes in 1975, output fell to 400,000 tonnes by the early 1990s. But since then the sugar industry has passed into private hands again. Over the past decade production has returned to its historic peak—and is now set to boom. The change has been gradual. The government has sold its stake in the industry in tranches. But now investors are piling in. As in other parts of South and Central America they are attracted by higher prices for sugar because of its use for ethanol. Industry sources predict that land under sugar will expand by 10,000 hectares (25,000 acres) a year, more than doubling output over the next decade. That would turn Peru into an exporter—though not on the scale of Brazil or Colombia. Last year, local investors secured a controlling stake in Casa Grande, the largest sugar plantation. Bioterra, a Spanish company, plans a $ 90m ethanol plant nearby. Maple, a Texas company, has bought 10,600 hectares of land in the northern department of Piura. Its plans call for an investment of $120m and ethanol production of 120m litres a year. Brazilian and Ecuadorean investors are also active. Part of the attraction is that Peru has signed a free-trade agreement with the United States. Provided that it can satisfy the concerns of the new Democratic-controlled Congress in Washington D. C., about the enforcement of labour rights, this agreement should be approved later this year. It would render permanent existing trade preferences under which ethanol from Peru can enter the United States dutyfree. By contrast, ethanol exported from Brazil, the world"s biggest producer, must pay a tariff of 54 cents a gallon. Two harsh realities might sour these sweet dreams. Colombia, Central America and the Dominican Republic all enjoy similar preferences and have similar plans. Colombia already produces 360m litres a year of ethanol, much of it for export. The second question is whether sugar—a thirsty crop—is the best use of Peru"s desert coastal strip, with its precarious water supply. One of the country"s achievements of the past decade has been the private sector"s development of new export crops. It would be ironic if these businesses were threatened by sugar"s privatisation. The word "precarious" (Paragraph 5) most probably means______.
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