Every animal sleeps,but the reason for this has remained foggy. When lab rats are not allowed to sleep, they die within a month.{#blank#}1{#/blank#} 

    One idea is that sleep helps us strengthen new memories. {#blank#}2{#/blank#} We  know that, while awake,fresh memories are recorded by reinforcing (加强)connections between brain cells, but the  memory processes that take place while we sleep  have been unclear.

    Support is growing for a theory that sleep evolved so that connections between neurons(神经元)in the brain can be weakened overnight, making room for fresh memories to form the next day.  {#blank#}3{#/blank#}

    Now we have the most direct evidence yet that he is right. {#blank#}4{#/blank#} The synapses in the mice taken at the end of a period of sleep were 18 per cent smaller than those taken before sleep,showing that the connections between neurons weaken while sleeping.

If Tononi's theory is right, it would explain why, when we miss a night's, we find it harder the next day to concentrate and learn new information —our brains may have smaller room for new experiences.

    Their research also suggests how we may build lasting memories over time even though the synapscs become thinner. The team discovered that some synapses seem to be protected and stayed the same size. {#blank#}5{#/blank#}  “You keep what matters,” Tononi says.

    If you can find a tree which has been cut down，you will see many rings，or circles，on the base of the trunk.By learning to read these rings，you can find out about the tree's life.

    The number of rings tells you how old the tree is.Each year，new wood is formed on the outside of the tree.This new wood is light in color when the tree is growing in spring and summer，and dark in winter when the tree is not growing much.So，if you count the rings of dark­or­light colored wood，you can often find out how old the tree is.

    You can also tell which years have been good years and which years have been bad years.When the light­colored rings are very wide，it means that the tree has been growing quickly that year.If the rings are narrow，it has been growing slowly.If the rings on a tree trunk were greatly magnified，you would be able to see why the rings are light­colored when the tree is growing quickly and dark­colored when the tree is growing slowly.The tree trunk is made up of microscopic tubes，like some pipes，carrying water from the soil，through the trunk，and up to the leaves.They are wide and thin­walled when the tree is growing quickly and they are carrying a lot of water.They are narrow and stuck together when the tree is not growing so quickly.

    When a tree is old，the tubes in the centre of the tree don't carry water.The walls of the tubes have become thick with materials which have stuck along them over the years，forming a kind of wood called“heartwood”．This kind of wood is darker in color than the young，growing wood on the outside of the tree.

    You don't very often see whole tree trunks which have been cut across.But once you learn to read a cross section of the wood，you can see much more in wood which has been used to make boxes，houses and other things.

    In most wood，instead of seeing the trunk cut across，you are seeing it cut along its length.Because you don't see the whole tree，you can't tell how old it is.

Title：{#blank#}1{#/blank#} of a Tree

    The Internet has opened up a whole new online world for us to meet, chat and go where we've never been before.

    But just as in face to face communication, there are some rules of behavior that should be followed when on line. {#blank#}1{#/blank#}  Imagine how you'd feel if you were in the other person's shoes. For anything you're about to send: ask yourself, “Would I say this to the person's face?” If the answer is no, rewrite and reread. {#blank#}2{#/blank#}

    If someone in the chat room is rude to you, your instinct(本能) is to fire back in the same manner. But try not to do so. {#blank#}3{#/blank#} If it was caused by a disagreement with another member, try to fix the situation by politely discussing it. Remember to respect the beliefs and opinions of others in the chat room.

    {#blank#}4{#/blank#} Offer advice when asked by newcomers, as they may not be sure what to do or how to communicate. When someone makes a mistake, whether it's a stupid question or an unnecessarily long answer, be kind about it. If it's a small mistake, you may not need to say anything. Even if you feel strongly about it, think twice before saying anything. Having good manners yourself doesn't give you license to correct everyone else. {#blank#}5{#/blank#} At the same time, if you find you are wrong, be sure to correct yourself and apologize to those that you have offended（冒犯）. It is not polite to ask others personal questions such as their age, sex and marital(婚姻的) status. Unless you know the person very well, and you are both comfortable with sharing personal information, don't ask such questions.

    The benefits of being an independent business are truly great. Beyond the rewarding nature of owning something truly unique, small businesses have the edge over their big business counterparts in many areas. Consider the importance of being independent and how that independence can help drive your business.

    To some, having fewer customers simply means less cash flow; however, having a smaller base also allows you to focus more on customer satisfaction.

    Companies are always searching for ways to improve customer service and have more of their business. Whether through paying special attention to who comes through your door or monitoring your customers through the social network, it's less of trouble to make sure your customers' needs are being met when there's a smaller sample to deal with. In addition, it becomes much easier to create a personal connection with buyers when you have enough time and attention to show them some love.

    Small businesses have an inherent advantage over their big box competitors in the sense that they can offer something different. People want to see the independent businesses that offer unique products and flavor to their communities. Your business can be the difference when it comes to what customers want.

    Of course, big box companies will almost always beat you down when it comes to price. Consider, however, that if you can offer a truly unique product or experience, price becomes much less of an issue.

    People like the idea of supporting local independent businesses versus “the big guys”. So, what businesses are booming due to the rise of independence?

Craft Beer(精酿啤酒) —- The craft beer movement in the United States is supported so widely that big breweries have taken to creating their own competing “craft beer” brands in an attempt to follow the trend. While Anheuser Busch represents nearly half of America's breweries, craft beer has seen a huge jump in sales in recent years.

Video Games —- Whether through PCs, traditional consoles or mobile games, independent developers are supported by enthusiastic fans and micro-transactions in an industry that was formerly dominated by bigger developers.

Musicians —- The modern web offers immense opportunities to musicians, resulting in more economic and artistic freedom. A surprising number of mainstream artists have seen great success from their independent releases, such as Macklemore's The Heist, which has sold over one million copies in the United States alone.

    Some small businesses don't want to be small businesses forever. Regardless, consider what independence does for you and your company. If you offer something out of the ordinary, you can build an audience that respects your individuality and supports your cause.

    Screen Time: How Much Is Too Much?

    Many children spend a lot of time watching or playing with electronic media—from televisions to video games, computers and other devices. {#blank#}1{#/blank#} Perhaps parents now should ease up on their concerns about screen time, at least for older boys and girls.

    Until last year, the American Academy of Pediatrics (AAP) suggested that children and teenagers have no more than two hours of screen time a day. It also suggests that parents balance a child's screen time with other activities.

    {#blank#}2{#/blank#} Christopher Ferguson, who teaches psychology at Stetson University in Florida, notes a lack of evidence supporting reports that too many hours spent playing video games or watching TV is truly harmful.

    Ferguson seems interested in one idea: the link between video games and violent or risky behavior. When he saw results from a recent British survey on screen time, he wanted to know more. The British study found a small negative effect—about a one percent increase—in aggression and depression among children who had six or more hours of screen time a day. {#blank#}3{#/blank#} So, Ferguson and his team examined answers from a survey on risky behaviors. The study involved about 6,000 boys and girls in Florida, whose average age was 16.

    Data from this survey found that American children are also fairly resistant to the negative effects of electronic media. Among those who used screens up to six hours a day, the survey found: a 0.5 percent increase in criminal behavior; a 1.7 percent increase in signs of depression; and a 1.2 percent negative effect on school grades. {#blank#}4{#/blank#} To further argue his point that screen time is not harmful, Ferguson adds that children should become familiar with screen technology. Electronic devices, he says, are a part of our everyday lives.

A. Some negative experiences on social media can and do affect some children.

B. However, some experts question claims that too much screen time is harmful.

C. He wanted to see if there was a similar effect among young people in the United States.

D. So, it is natural that parents should wonder about all the time children spend looking at a screen.

E. The researchers found no increase in risky sex or driving behaviors, use of illegal substances or eating disorders.

F. The researchers suggested that for those children, technology use might get in the way of taking part in other important activities.

    This time of year, thousands of college applicants wait for e­notices and auspiciously(吉利地) sized envelopes from schools, under terrible pressure from their parents, friends, teachers, and themselves. As to this, I offer some advice, which comes not only from a bit of experience, but also a bit of research: just cool out and continue, okay?

    Many parents and students think there is a world of difference between the lifelong outcomes of an A­minus student who gets into, say. Princeton, and an A­minus student who applies to Princeton but "only" gets into some less selective school, like Penn State or the University of Wisconsin. They assume that a decision made by faceless Ivy League admissions officers, to some extent, will mark the difference between success and failure in life.

    There are two important things to say about this stress. First, to put the anxiety into context, the kids applying to these schools are already doing quite well. Seventy percent of 29­-year-­olds don't have a bachelor's degree, and the majority of BAs are earned at non­selective schools that accept a majority of their applicants. Many of the applicants have already won life's lottery.

    But if that doesn't ease the nerves of the 40,000 people waiting on Stanford or Penn, here is a more encouraging conclusion from economics. For most applicants, it doesn't matter if they don't get into their top choice, according to a paper by Stacy Dale, a mathematician at Mathematica Policy Research, and Alan Krueger, an economist at Princeton University. They tracked two groups of students——­one that attended college in the 1970s and the other in the early 1990s. They wanted to know：Did students attending the most elite colleges earn more in their 30s. 40s. and 50s than students with similar SAT scores, who were rejected by elite colleges? The short answer was no. Or, in the author's language, the difference between the students who went to super­selective schools and the students with similar SAT scores rejected by those schools and went to less selective institutions was "indistinguishable from zero."

    What does that mean? It means that, for many students, "who you are" is more important than where you go. It's hard to show that highly selective colleges add much earning power, even with their distinguished professors and professional networks. In addition, the decision of admissions officers isn't as important as the sum of the decisions, habits, and relationships students have built up to this point in their young life.

    For the elite colleges themselves, the Dale­Krueger paper had additional, fascinating findings. It's found that the most selective schools do make an extraordinary difference in life earning for minority students from less-­educated families who are more likely to rely on colleges to provide the training and job networks with great influence. Getting into Princeton if your parents went to Princeton? Fine, although not a game­changer.  But getting into Princeton if your parents both left community college after a year? That could be game­changing. Whatever the results, it's more important to choose a university that is suited to the college applicants.