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SNMP协议实体发送请求和应答报文的默认端口号是（46），采用UDP提供数据报服务，原因不包括（47）。（46）A.160B.161C.162D.163（47）A.UDP数据传输效率高B.UDP面向连接，没有数据丢失C.UDP无需确认,不增加主机重传负担 D.UDP开销小,不增加网络负载

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某公司网络的地址是192.168.192.0/20，要把该网络分成32个子网，则对应的子网掩码应该是（54），每个子网可分配的主机地址数是（55）。（54）A.255.255.252.0B.255.255.254.0C.255.255.255.0D.255.255.255.128（55）A.62B.126C.254D.510

With circuit switching, a （71）path is established between two stations for communication . Switching and transmission resources within the network are （72）for the exclusive use of the circuit for the duration of the connection . The connection is（73）：Once it is established ，it appears to attached devices as if there were a direct connection. Packet switching was designed to provide a more efficient facility than circuit switching for（74）data traffic. Each packet contains some portion of the user data pluscontrol information needed for proper functioning of the network. A key distinguishing element of packet-switching networks is whether the internal operation is datagram or virtual circuit . With internal virtual circuits,a route is defined between two endpoints and all packets for that virtual circuit follow the（75）route, With internal datagrams,each packet is treated independently,and packets intended for the same destination may follow different routes.（71）A.uniqueB.dedicatedC.nondedicated D.independent（72）A.discarded B.abandonedC.reserved D.broken（73）A.indistinct B.directC.indirect D.transparent（74）A.casualB.burstyC.limited D.abundant（75）A.sameB.differentC.single D.multiple

Is Breakfast Really the Most Important Meal of the Day?A) Along with old classics like "carrots give you night vision" and "Santa doesn't bring toys to misbehaving children", one of the most well-worn phrases of tired parents everywhere is that breakfast is the most important meal of the day. Many of us grow up believing that skipping breakfast is a serious mistake, even if only two thirds of adults in the UK eat breakfast regularly, according to the British Dietetic Association, and around three-quarters of Americans.B) "The body uses a lot of energy stores for growth and repair through the night," explains diet specialist Sarah Elder. "Eating a balanced breakfast helps to up our energy, as well as make up for protein and calcium used throughout the night." But there's widespread disagreement over whether breakfast should keep its top spot in the hierarchy (等级) of meals. There have been concerns around the sugar content of cereal and the food industry's involvement in pro-breakfast research -- and even one claim from an academic that breakfast is "dangerous".C) What's the reality? Is breakfast a necessary start to the day or a marketing tactic by cereal companies? The most researched aspect of breakfast(and breakfast-skipping) has been its links to obesity. Scientists have different theories as to why there's a relationship between the two. In one US study that analysed the health data of 50,000 people over seven years, researchers found that those who made breakfast the largest meal of the day were more likely to have a lower body mass index (BMI) than those who ate a large lunch or dinner. The researchers argued that breakfast helps reduce daily calorie intake and improve the quality of our diet -- since breakfast foods are often higher in fibre and nutrients.D) But as with any study of this kind, it was unclear if that was the cause -- or if breakfast-skippers were just more likely to be overweight to begin with. To find out, researchers designed a study in which 52 obese women took part in a 12-week weight loss programme. All had the same number of calories over the day, but half had breakfast, while the other half did not. What they found was that it wasn't breakfast itself that caused the participants to lose weight: it was changing their normal routine.E) If breakfast alone isn't a guarantee of weight loss, why is there a link between obesity and breakfast-skipping? Alexandra Johnstone, professor of appetite research at the University of Aberdeen, argues that it may simply be because breakfast-skippers have been found to be less knowledgeable about nutrition and health. "There are a lot of studies on the relationship between breakfast eating and possible health outcomes, but this may be because those who eat breakfast choose to habitually have health-enhancing behaviours such as regular exercise and not smoking," she says.F) A 2016 review of 10 studies looking into the relationship between breakfast and weight management concluded there is "limited evidence" supporting or refuting (反驳) the argument that breakfast influences weight or food intake, and more evidence is required before breakfast recommendations can be used to help prevent obesity.G) Researches from the University of Surrey and University of Aberdeen are halfway through research looking into the mechanisms behind how the time we eat influences body weight. Early findings suggest that a bigger breakfast is beneficial to weight control. Breakfast has been found to affect more than just weight. Skipping breakfast has been associated with a 27% increased risk of heart disease, a 21% higher risk of type 2 diabetes in men, and a 20% higher risk of type 2 diabetes in women. One reason may be breakfast's nutritional value -- partly because cereal is fortified (增加营养价值) with vitamins. In one study on the breakfast habits of 1,600 young people in the UK, researchers found that the fibre and micronutrient intake was better in those who had breakfast regularly. There have been similar findings in Australia, Brazil, Canada and the US.H) Breakfast is also associated with improved brain function, including concentration and language use. A review of 54 studies found that eating breakfast can improve memory, though the effects on other brain functions were inconclusive. However, one of the review's researchers, Mary Beth Spitznagel, says there is "reasonable" evidence breakfast does improve concentration -- there just needs to be more research. "Looking at studies that tested concentration, the number of studies showing a benefit was exactly the same as the number that found no benefit," she says. "And no studies found that eating breakfast was bad for concentration."I) What's most important, some argue, is what we eat for breakfast. High-protein breakfasts have been found particularly effective in reducing the longing for food and consumption later in the day, according to research by the Australian Commonwealth Scientific and Industrial Research Organisation. While cereal remains a firm favourite among breakfast consumers in the UK and US, a recent investigation into the sugar content of 'adult' breakfast cereals found that some cereals contain more than three-quarters of the recommended daily amount of free sugars in each portion, and sugar was the second or third highest ingredient in cereals.J) But some research suggests if we're going to eat sugary foods, it's best to do it early. One study recruited 200 obese adults to take part in a 16-week-long diet, where half added dessert to their breakfast, and half didn't. Those who added dessert lost an average of 40 pounds more -- however, the study was unable to show the long-term effects. A review of 54 studies found that there is no consensus yet on what type of breakfast is healthier, and concluded that the type of breakfast doesn't matter as much as simply eating something.K) While there's no conclusive evidence on exactly what we should be eating and when, the consensus is that we should listen to our own bodies and eat when we're hungry. "Breakfast is most important for people who are hungry when they wake up," Johnstone says. "Each body starts the day differently -- and those individual differences need to be researched more closely," Spitznagel says. "A balanced breakfast is really helpful, but getting regular meals throughout the day is more important to leave blood sugar stable through the day, which helps control weight and hunger levels," says Elder. "Breakfast isn't the only meal we should be getting right."1. () According to one professor, obesity is related to a lack of basic awareness of nutrition and health.2. () Some scientists claim that people should consume the right kind of food at breakfast.3. () Opinions differ as to whether breakfast is the most important meal of the day.4. () It has been found that not eating breakfast is related to the incidence of certain diseases in some countries.5. () Researchers found it was a change in eating habits rather than breakfast itself that induced weight loss.6. () To keep oneself healthy, eating breakfast is more important than choosing what to eat.7. () It is widely considered wrong not to eat breakfast.8. () More research is needed to prove that breakfast is related to weight loss or food intake.9. () Pecople who prioritise breakfasts tend to have lower calorie but higher nutritional intake.10. () Many studies reveal that eating breakfast helps people memorise and concentrate.

The quiet heroism of mail deliveryA) On Wednesday, a polar wind brought bitter cold to the Midwest. Overnight, Chicago reached a low of 21 degrees Fahrenheit below zero, making it slightly colder than Antarctica (南极洲), Alaska, and the North Pole. Wind chills were 64 degrees below zero in Park Rapids, Minnesota, and 45 degrees below zero in Buffalo, North Dakota, according to the National Weather Service. Schools, restaurants, and businesses closed, and more than 1,000 flights were canceled.B) Even the United States Postal Service (USPS) suspended mail delivery. "Due to this arctic outbreak and concerns for the safety of USPS employees," USPS announced Wednesday morning, "the Postal Service is suspending delivery Jan. 30 in some 3-digit ZIP Code locations." Twelve regions were listed as unsafe on Wednesday; on Thursday, eight remained.C) As global surface temperatures increase, so does the likelihood of extreme weather. In 2018 alone, wildfires, volcanic eruptions, hurricanes, mudslides, and other natural disasters cost at least $49 billion in the United States. As my colleague Vann Newkirk reported, Puerto Rico is still confronting economic and structural destruction and resource scarcity from 2017's Hurricane Maria. Natural disasters can wreck a community's infrastructure, disrupting systems for months or years. Some services, however, remind us that life will eventually return, in some form, to normal.D) Days after the deadly 2017 wildfires in Santa Rosa, California, a drone (无人机) caught footage (连续镜头) of a USPS worker, Trevor Smith, driving through burned homes in that familiar white van, collecting mail in an affected area. The video is striking: The operation is familiar, but the scene looks like the end of the world. According to Rae Ann Haight, the program manager for the national-preparedness office at USPS, Smith was fulfilling a request made by some of the home owners to pick up any mail that was left untouched. For Smith, this was just another day on the job. "I followed my route like I normally do," Smith told a reporter. "As I came across a box that was up but with no house, I checked, and there was mail -- outgoing mail -- in it. And so I picked those up and carried on."E) USPS has sophisticated emergency plans for natural disasters. Across the country, 285 emergency-management teams are devoted to crisis control. These teams are trained annually using a framework known as the three Ps: people, property, product. After mail service stops due to weather, the agency's top priority is ensuring that employees are safe. Then it evaluates the health of infrastructure, such as the roads that mail carriers drive on. Finally, it decides when and how to re-open operations. If the destruction is extreme, mail addressed to the area will get sent elsewhere. In response to Hurricane Katrina in 2005, USPS redirected incoming New Orleans mail to existing mail facilities in Houston. Mail that was already processed in New Orleans facilities was moved to an upper floor so it would be protected from water damage.F) As soon as it's safe enough to be outside, couriers (邮递员) start distributing accumulated mail on the still-accessible routes. USPS urges those without standing addresses to file change-of-address forms with their new location. After Hurricane Katrina hit in 2005, mail facilities were set up in dozens of locations across the country in the two weeks that USPS was unable to provide street delivery.G) Every day, USPS processes, on average, 493.4 million pieces of mail -- anything from postcards to Social Security checks to medicine. Spokespeople from both USPS and UPS told me all mail is important. But some mail can be extremely sensitive and timely. According to data released in January 2017, 56 percent of bills are paid online, which means that just under half of payments still rely on delivery services to be completed.H) It can be hard to identify which parcels are carrying crucial items such as Social Security checks, but USPS and UPS try their best to prioritize sensitive material. They will coordinate with the Social Security Administration to make sure that Social Security checks reach the right people in a timely fashion. After Hurricane Florence and Hurricane Michael last fall, USPS worked with state and local election boards to make sure that absentee ballots were available and received on time.I) Mail companies are logistics (物流) companies, which puts them in a special position to help when disaster strikes. In a 2011 USPS case study, the agency emphasized its massive infrastructure as a "unique federal asset" to be called upon in a disaster or terrorist attack. "I think we're unique as a federal agency," USPS official Mike Swigart told me, "because we're in literally every community in this country... We're obligated to deliver to that point on a daily basis."J) Private courier companies, which have more dollars to spend, use their expertise in logistics to help revitalize damaged areas after a disaster. For more than a decade, FedEx has supported the American Red Cross in its effort to get emergency supplies to areas affected by disasters, both domestically and internationally. In 2012, the company distributed more than 1,200 MedPacks to Medical Reserve Corps groups in California. They also donated space for 3.1 million pounds of charitable shipping globally. Last October, the company pledged $1 million in cash and transportation support for Hurricanes Florence and Michael. UPS's charitable arm, the UPS Foundation, uses the company's logistics to help disaster-struck areas rebuild. "We realize that as a company with people, trucks, warehouses, we needed to play a larger role," said Eduardo Martinez, the president of the UPS Foundation. The company employs its trucks and planes to deliver food, medicine, and water. The day before I spoke to Martinez in November, he had been touring the damage from Hurricane Michael in Florida with the American Red Cross. "We have an obligation to make sure our communities are thriving," he said.K) Rebuilding can take a long time, and even then, impressions of the disaster may still remain. Returning to a normal life can be difficult, but some small routines -- mail delivery being one of them -- may help residents remember that their communities are still their communities. "When they see that carrier back out on the street," Swigart said, "that's the first sign to them that life is starting to return to normal."1. () The United States Postal Service has a system to ensure its employees' safety.2. () One official says USPS is unique in that it has more direct reach to communities compared with other federal agencies.3. () Natural disasters can have a long-lasting impact on community life.4. () Mail delivery service is still responsible for the completion of almost half of payments.5. () The sight of a mailman on the street is a reassuring sign of life becoming normal again.6. () After Hurricane Katrina interrupted routine delivery, temporary mail service points were set up.7. () Postal service in some regions in the U.S. was suspended due to extreme cold weather.8. () Private postal companies also support disaster relief efforts by distributing urgent supplies.9. () A dedicated USPS employee was on the job carrying out duties in spite of extreme conditions.10. () Postal services work hard to identify items that require priority treatment.