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.

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    Here is a list of some of the best museums for children in America.

    Please Touch Children's Museum

    This museum lies in Philadelphia. It offers Alice in Wonderland exhibits where young children can play with giant flowers and have tea parties. Kids can also play on musical instruments and babies can crawl on lily pads, which make musical sounds.

    The Children's Museum of Indianapolis

    This museum lies in Indiana. It holds a fair share of dinosaur fossils (化石). There are many fossils like the T. Rex, Bucky and many others in an 8,000-square-foot area. Around 10,000 man-made objects, including a 55-ton steam engine and a 33-foot tall water clock, are there in the 365,000-square-foot area. It also offers activities like dinosaur building, camps and classes featuring space themes and other educational programs.

    Boston Children's Museum

    This museum lies in Massachusetts. The exhibits here are of health, art, science, culture and environment. In this museum, children also learn about Japanese culture. Activities like Play Lab, New Balance Climb and The Recycle Shop bring out the creativity in children.

    National Museum of Play

    This museum, which lies in Rochester area of New York, has a wide collection of dolls, games, toys and other home crafts dating back to the 19th century. Here, educational tours include stories of machines and other toys. Kids can walk in Sesame Street exhibit and cook food at play or TV studios.

    Children's Museum of Houston

    This museum lies in Texas. Termed as the best playground for mind, this museum offers scores of activities for kids of every age. It even offers free family adventure events where families with their kids are encouraged to work on math activities and games. Children also learn about broadcasting activities and preserving ecosystems.

    “The world feels anxious and divided, and Facebook has a lot of work to do whether it's protecting our community from abuse and hate, defending against interference by nation states, or making sure that time spent on Facebook is well spent,” Zuckerberg wrote on Facebook in January.

    If the tech firm succeeded, Facebook would end 2018 on a much better path. But the cracks in Zuckerberg's social media empire only grew as scandals(丑闻)about data misuse, security and even Facebook's leadership piled up.

    The social network has faced criticism many times since launching 14 years ago, but the public uproar reached new heights in 2018. Facebook's missteps, even as it tried to fix its problems, were yet another reminder of what happens when a company grows rapidly with little oversight(监管). They also set the stage for another showdown between the tech powerhouse and lawmakers who have their own ideas on how to manage a platform used by 2.3 billion people every month.

    “I think there's just a general growing consensus from both parties in Congress that self-policing is not going to work,” Democratic senator Mark Warner of Virginia said in an interview. Facebook pointed to a series of notes Zuckerberg published this year outlining what the tech firm has done to combat(战斗，争论)election meddling(好干预的), as well as hate speech, misinformation and other offensive content. The social network pulled down more than 1.5 billion fake accounts, launched a database of political ads and announced the creation of a Supreme Court like independent body to oversee content appals.

    But in many ways, Zuckerberg fell short of his New Year's resolution(决议). UN investigators said Facebook played a role in spreading hate speech that fueled ethnic cleansing(清洗)in Myanmar. Media outlets found loopholes(漏洞)and errors in Facebook's political ads database. Users questioned whether they should delete Facebook after learning that Cambridge Analytical, a UK political consulting firm with ties to Donald Trump's 2016 presidential campaign, gathered data on as many as 87 million Facebook users without their permission.

    In short, Facebook's problems ballooned out of the company's control.

“They created a platform where sharing was mindlessly easy and interacting with each other required almost no forethought at all,” said Woodrow Hertzog, a law and computer science professor at Northeastern University. “As a result, there was massive sharing, including leaking of personal information that put lots of people at risk.”

    Below you will find a profile of each gap year program. If there is a specific program you are interested in or a question you have regarding these programs, please feel free to contact them directly.

    Youth International

    Since 1997, Youth International has been providing many people with the most exciting and educational experience of their life. It is a learning program that combines international travel, inter-cultural exchange, home stays, volunteer community service work and outdoor adventures.

    Phone: 720-270-3323

    Carpe Diem Education

    Through volunteer service, travel and cultural exchange, students of Carpe Diem Education receive a personal insight into themselves and their cultures. We specialize in guiding summer and semester programs for high school students. Each course is carefully crafted to develop leadership and self-awareness within our students, who return home better prepared to be leaders in thought and action.

    Phone: 503-285-1800

    Center for Interim Programs

    Founded in 1980, Center for Interim Programs is the first independent gap-year organization in America. Based on students' interests and budget, our experienced teachers help make individual course choices including: low cost volunteer options, language programs, research trips, and so on. We are committed to helping students find more experiences of formal education and work.

    Phone: 413-585-0980

    EF Gap Year

    EF Gap Year offers students the ability to explore several countries where you will learn a language, volunteer for a good cause, gain international work experience. Choose between a 12-week semester or 26-week academic year. You can then personalize your program to meet your learning goals and interests by deciding where, when, and how you wish to study on your own. Our well-structured curriculum even allows you to place out of college-level classes and earn advanced credits toward graduation.

    Phone: 800-726-9746

    When you're on the go, your best friend and resource can be your phone. In the age of smart phones, apps are like guiding stars: They can point you in the right direction for a hotel, list expenses, send postcards, and much more. When used together, these apps can be the basic travel tool, placing a wealth of information at your fingertips no matter where you are on the planet. U.S. News Travel has picked the essential travel apps, known for their utility and reliability. Best of all, they cost absolutely nothing.

    Trip It

    Your Personal Travel Agent

    Be your own travel agent and plan every detail of your trip-- from car rental to accommodating restaurants-- with Trip It. You can make travel schedule by hand, or simply forward the email confirmations of your flight, rental car, train tickets, and hotels to plans.

Weather Free

    Your Go-To Meteorologist(气象学者)

    Stop trying to explain the weather forecast on the evening news (particularly when it's in a foreign language.) The Weather Free app informs you (in English) of the climate in various locations. It features the local weather, and other key factors that will inform your decision about what to wear before stepping outside.

    Goby

    Your Event Guru

    When you're in a foreign city, you sometimes look around and ask: Where are all the people? Goby has the answer. This app pinpoints the neighborhood hot spots (including museums, hotels, eateries, and more) in your neighborhood. But its true value comes in finding nearby events. You'll discover concerts, plays, and more right around the corner.

    It has been described as art by some people, but to others it's an ugly part of modern life. What is it? Graffiti (涂鸦), of course. Look around cities in the UK today and you can see graffiti on buildings, walls, doors and even on buses or trains that have stayed in one place for too long. But where modern technology creates a problem, it also finds a way to deal with it. Last week, The Weekend West was shown around the factory of a small but successful company, Hubdean.

    Hubdean's achievement is a series of special paints which are graffiti-resistant. How do they work? It couldn't be simpler. Take any graffiti-covered surface. First, a treatment called Agproclear is used. Then, using a very hot pressure jet (压力喷嘴), this treatment is taken away and the graffiti disappears at the same time. Now you have a clean wall. But before this clean wall can be painted on by graffiti lovers, a new product, Agproshield, is used. This paint has a special surface which gives it two important advantages. Firstly, spray paint (喷雾颜料) won't stick to the surface very well, and secondly, the whole surface can be cleaned very easily, just using water. Once the surface is painted, no specialist equipment is needed to keep the area clean and graffiti-free.

    Not surprisingly, Hubdean's products are used by both local governments and private companies all over the UK, and now orders are being received from around the world. This brings the company a problem, however. Can they increase production to satisfy the needs? Of course, they can build a second factory or work with a large international company to make their products. The future is looking good for Hubdean!