Think about the different ways that people use the wind. You can use it to fly a kite or to sail a boat. Wind is one of our cleanest and richest power sources, as well as one of the oldest. Evidence shows that windmills(风车) began to be used in ancient Iran back in the 7th century BC. They were first introduced to Europe during the 1100s, when armies returned from the Middle East with knowledge of using wind power.

    For many centuries, people used windmills to grind(磨碎) wheat into flour or pump water from deep underground. When electricity was discovered in the late 1800s, people living in remote(偏远的) areas began to use them to produce electricity. This allowed them to have electric lights and radio. However, by the 1940s when electricity was available(可利用的) to people in almost all areas of the United States, windmills were seldom used.

    During the 1970s, people started becoming concerned about the pollution that is created when coal and gas are burned to produce electricity. People also realized that the supply of coal and gas would not last forever. Then, wind was rediscovered, though it means higher costs. Today, there is a global movement to supply more and more of our electricity through the use of wind.

根据短文内容，选择最佳答案，并将选定答案的字母标号填在题前括号内。

    Can exercise during childhood protect you against memory loss many decades later?Exercise early in life seems to have lifelong benefits for the brain,in rats at least.

     “This is an animal study,but it shows that physical activity at a young age is very important—not just for physical development,but for the whole lifelong track of cognitive（认知的）development during ageing,”says Martin Wojtowicz of the University of Toronto,Canada.“In humans,it may delay the appearance of Alzheimer's symptoms（阿茨海默氏症）,possibly to the point of preventing them.”

    Wojtowicz's team divided 80 young male rats into two equal groups,and placed running wheels in the cages of one group for a period of six weeks.Around four months later—when the rats had reached middle age—the team taught all the rats to connect an electric shock with being in a specific.When placed in the box,they froze with fear.

    Two weeks later,the team tested the rats in three situations: exactly the same box in the same room,the same box with the room arranged differently,and a completely different box in a different room.

    The rats without access to a running wheel when they were young now froze the same percentage of times in each of these situations,suggesting they couldn't remember which one was dangerous.But those that had been able to run in their youth froze 40 to 50 percent less in both changed box settings.

    "The results suggest the amount of physical activity when we're young,at least for rats,has influence on brain and cognitive health—in the form of better memories—when we're older,"says Arthur Kramer of Northeastern University in Boston,who has found that,in humans,exercise promotes the growth of new brain cells.

    Internet Security Awareness

    MS-ISAC

    “Kids Safe Online”

    2017 Virginia Poster Contest(比赛)

    Official Rules

    Contestants

    The contest is open to all Virginia public, private Kindergarteners -12 in the United States, District of Columbia and the U.S. Territories (领土).

    Judging Criteria

    Posters will be judged on the following criteria:

    Clear message conveyed by the text and artwork

    Creativity, originality and artistic quality

    Visual clarity - easily read

    Bright and colorful

    Must not use published materials.

    Winners

    Virginia will select the top 5 winning posters from each grade group (K-5, 6-8, 9-12) and send them to the National Multi-State Information Sharing and Analysis Center (MS-ISAC) Internet Security Awareness Poster Contest. The Virginia winners will receive a certificate of appreciation. MS- ISAC will select four winners in each grade and award a prize. These winners will have the honor of having their artwork made into a poster calendar which will be handed out throughout the country and may also be used in campaigns to raise awareness among children of all ages about the Internet.

    Posters will not be returned!

    Deadline

    All posters must be received by midnight, Jan. 6, 2017.

    Poster should be mailed to:

    Kids Safe Online Poster Contest Virginia Information Technology Agency Commonwealth Security & Risk Management

    11751 Meadowville Lane Chester, VA 23836

    Electronic posters can be sent to: CommonwealthSecurity@virginia.gov

    Contest Timeline

    Now through Jan. 6, 2017

    Students create their posters and the school can choose up to 15 posters to send to VITA by midnight January 6, 2017.

    No Later than Jan. 27, 2017

    Virginia posters will be judged and the top 15 posters will be sent to MS-ISAC for national judging.

    Jan. 30 to March 3, 2017,

    MS-ISAC will perform national judging. Winners will be declared no later than March 24, 2017

    Facial expressions carry meaning that is determined by situations and relationships. For example, in American culture the smile is in general an expression of pleasure. Yet it also has other uses. A woman's smile at a police officer does not carry the same meaning as the smile she gives to a young child. A smile may show love or politeness. It can also hide true feelings. It often causes confusion (困惑) across cultures. For example, many people in Russia consider smiling at strangers in public to be unusual and even improper. Yet many Americans smile freely at strangers in public places (although this is less common in big cities). Some Russians believe that Americans smile in the wrong places; some Americans believe that Russians don't smile enough. In Southeast Asian culture, a smile is frequently used to cover painful feelings. Vietnamese people may tell a sad story but end the story with a smile.

    Our faces show emotions (情感), but we should not try to "read" people from another culture as we would "read" someone from our own culture. The fact that members of one culture do not express their emotions as openly as members of another do does not mean that they do not experience emotions. Rather, there are cultural differences in the amount of facial expressions permitted. For example, in public and in formal situations many Japanese do not show their emotions as freely as Americans do. When with friends, Japanese and Americans seem to show their emotions similarly.

    It is difficult to make a general statement about Americans and facial expressiveness because of personal and cultural differences in the United States. People from certain cultural backgrounds in the United States seem to be more facially expressive than others. The key is to try not to judge people whose ways of showing emotion are different. If we judge according to our own cultural habits, we may make the mistake of "reading" the other person incorrectly.

    Almost every machine with moving parts has wheels, yet no one knows exactly when the first wheel was invented or what it was used for. We do know, however, that they existed over 5,500 years ago in ancient Asia.

    The oldest known transport wheel was discovered in 2002 in Slovenia. It is over 5,100 years old. Evidence suggests that wheels for transport didn't become popular for a while, though. This could be because animals did a perfectly good job of carrying farming tools and humans around.

    But it could also be because of a difficult situation. While wheels need to roll on smooth surfaces, roads with smooth surfaces weren't going to be constructed until there was plenty of demand for them. Eventually, road surfaces did become smoother, but this difficult situation appeared again a few centuries later. There had been no important changes in wheel and vehicle design before the arrival of modem road design.

    In the mid-1700s, a Frenchman came up with a new design of road—a base layer (层) of large stones covered with a thin layer of smaller stones. A Scotsman improved on this design in the 1820s and a strong, lasting road surface became a reality. At around the same time, metal hubs (the central part of a wheel) came into being, followed by the pneumatic tyre (充气轮胎) in 1846. Alloy wheels were invented in 1967, sixty years after the appearance of tarmacked roads (柏油路). As wheel design took off, vehicles got faster and faster.

    There are two main things that make aircraft engineering difficult: the need to make every component as reliable as possible and the need to build everything as light as possible. The fact that an airplane is up in the air and can't stop if anything goes wrong, makes it perhaps a matter of life or death that its performance is completely dependable.

    Given a certain power of engine, and consequently a certain fuel consumption, there is a practical limit to the total weight of aircraft that can be made to fly. Out of that weight as much as possible is wanted for fuel, radio navigational instruments, passenger seats, or freight room, and of course, the passengers or freight themselves. So the structure of the aircraft has to be as small and light as safety and efficiency will allow. The designer must calculate the normal load that each part will bear. This specialist is called the "stress man." He takes notice of any unusual stress that may be put on the part as a precaution against errors in manufacture, accidental damage etc.

    The stress man's calculations go to the designer of the part, and he must make it as strong as the stress man says is necessary. One or two small parts are always tested to prove that they are as strong as the designer intended. Each separate part is tested, then a whole assembly—for example, a complete wing, and finally the whole aeroplane. When a new type of aeroplane is being made, normally only one of the first three made will be flown. Two will be destroyed on the ground in strict tests. The third one will be tested in the air.

    When a plane has passed all the tests it can get a government certificate of airworthiness, without which it is illegal to fly, except for test flying.

    Making the working parts reliable is as difficult as making the structure strong enough. The flying controls, the electronic equipment, the fire precautions, etc. must not only be light in weight, but must work both at high altitudes where the temperature may be below freezing point and in the hot air of an airfield in the tropics.

    To solve all these problems the aircraft industry has a large number of research workers, with elaborate laboratories and test houses, and new materials to give the best strength in relation to weight are constantly being tested.