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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    I must have looked deep in thought, or as deep in thought as an 11-year-old man can, when my grandmother glanced up from her weeding to ask, "You have something on your mind, don't you?"

    "Yes, I was thinking that someday I want to be an Olympic speedskating champion like my hero, Eric Heiden, I want to be a doctor like my parents and I want to help children in Africa."

    I immediately knew I had confided in the right person when a knowing smile broke across her face. "Johann, of course! You can do anything you want to do!" she said simply. And with my grandmother's support, I set out to pursue my passions.

    14 years later, I was well ready to take hold of my first dream: becoming an Olympic champion. The Olympics in 1994 were in my home country, Norway. As I entered the Olympic stadium, I wasn't the best athlete, and many had doubts about my ability to perform well. But I had something special working for me. I had a woman in the first row who believed in me following my passions just as much as I did. For the first time ever, my grandmother was going to see me skate.

    It happened. Breaking a world record, I won the gold.

    As I stood on the podium(领奖台) that I had dreamed about my entire life, a curious question popped into my head. Why me? Why did I win, given all the other incredible competitors out there? The reason had to be more than a grandmother who shared a belief in her grandson's dream. The question led me to only one answer: because I wanted to make a difference in the world, and with all the media attention on my success, I could.

    I immediately knew what that difference had to be: hope in the lives of the children in Africa. Six months earlier, I'd been invited to Egypt as an ambassador for Olympic Aid.

    If you are taking vitamin supplements to reduce your risk of heart disease or cancer, a group of health experts want you to know that those vitamins may actually increase your risk of cancer.

The US Preventive Services Task Force came to this conclusion after reviewing dozens of studies. Nearly half of adults in the US take at least one vitamin or mineral supplement on a regular basis. These pills are advertised as a way to promote general health. In some cases, producers promote them as cancer fighters and heart protectors.

    Studies in animals and in laboratory dishes suggest that oxidative(氧化性的) stress contributes to diseases like cancer and heart disease. If so, there is a reason to believe that antioxidants—including beta－carotene, vitamins A, C, and E—could be useful as preventive medicines.

    But when the Task Force examined the medical evidence on vitamins, it found "inadequate(不充分的) evidence" to support the claims that vitamin and mineral supplements benefit healthy adults.

    "Cardiovascular(心血管的) disease and cancer have a significant health impact in America, and we all want to find ways to prevent these diseases，" Dr. Virginia Moyer, who heads the Task Force, said in a statement. But so far, she added, the medical evidence does not show that taking vitamins is helpful in this aspect.

    However, the Task Force did find "adequate evidence" that people with a raised risk for lung cancer actually increase their risk further by taking beta－carotene, a precursor of vitamin A.

The Task Force recommendations of taking vitamins regularly apply to healthy adults aged 50 and older who don't have "special nutritional needs". The advice does not apply to children, women who are pregnant or may become pregnant, people with chronic illnesses, or people who have to take supplements because they can't get all their essential nutrients from their diet.

72 hours in Beijing

    Traveling to China is no longer a luxury for many foreign passport holders. The Chinese government has permitted a 72-hour visa-free policy that offers access to visitors from 53 countries including the US, France and Austria. Let's start with the capital of China, Beijing Here's a pick of the best in Beijing!

    Mutianyu Great Wall

    Your trip to Beijing isn't really complete without seeing one of the "New Seven Wonders of the World", the Great Wall of China. The Mutianyu section of the Great Wall is by far the most well-preserved of all. Taking a one hour bus ride, Mutianyu would be your ideal location for a half-day of hiking away from the large crowds in the city. Also, the authorities have allowed tourists to paint graffiti on a specific section of the Great Wall since 2014. The Great Wall was designated a UNESCO World Heritage site in 1987.

    798 Art Zone

    This would be on the top of my list! Named after the 798 factory that was built in the 1950s, the art zone is home to various galleries, design studios, art exhibition spaces, fashionable shops and bars. You could easily spend half your day wandering around the complex, feeling the contrast of the present and the past.

    Summer Palace

    Located in northwestern Beijing, the Summer Palace is by far the city's most well-preserved royal park. With its huge lake and hilltop views, the palace offers you a pastoral escape into the landscape of traditional Chinese paintings. The Summer Palace was added to the UNESCO World Heritage List in 1998.

    Sichuan Provincial Restaurant

    While in Beijing, apart from trying the city's best-known Peking duck, the Sichuan provincial restaurant is one of places where you can enjoy regional delicious food. It offers one of China's eight great cuisines, Sichuan, which ranges from Mapo tofu to spicy chicken.

    I study English literature at university and have always been proud of Britain's literary heritage(文学遗产). Some British authors that you may have heard of are Charles Dickens and Jane Austen. These writers are famous all over the world because their books have been translated into many different languages. In the UK, their novels are celebrated as some of the best that have ever been written. We say that these novels are "classic" because they are still read and enjoyed years after their publication.

    I read classic novels because they are part of my university lessons but also because I enjoy them. They can teach you a lot about how people used to live and what society was like in the past. Novels like Hard Times by Charles Dickens remind us of the poverty in London during the Industrial Revolution while Jane Austen's fiction shows us what family life was like in the 18th century.

    Classic novels usually have memorable stories land interesting characters. One of my favourite books is Charles Dickens Great Expectations. It is about a boy called Pip who suddenly receives a lot of money from a mysterious supporter. As he grows up, his character changes: he becomes quite selfish and mean. Another important character is Miss Havisham. When she was young, her fiancé ran away on their wedding day. She lives in a dark house and still wears her wedding dress. She is a fascinating character, both sad and scary.

    Reading classic novels enriches my knowledge and life experience. And it has become part of life.

Family Fun

    Not only is Buffalo family-friendly, we're also family-fun! If you have yet to pack the car, here are four activities to plan for your next family adventure in Buffalo.

    Animal House

    Take a walk on the wild side and visit with our animal friends! You can have some facetime with river otters (水獭) at the Buffalo Zoo. Get up close and personal with animals on a tour at Hidden Valley Animal Adventure, and develop your child's sense of wonder at Tifft Nature Preserve, a place that's great for bird-watching. And don't leave town without a visit to the Aquarium of Niagara to see the penguins (企鹅)!

    Make a Splash

    Buffalo is surrounded by water and plenty of chances to make a splash. Head to Canalside and ride on a water bike or take a sunset tour on the Miss Buffalo II. Have fun in the water park at Fantasy Island or jump on a Whirlpool Jet Boat or a Niagara Jet Adventure tour for a wild ride on the Niagara River. Welcome to our water world.

    Hands-On Experiences

    Throw the textbooks aside and introduce your little explorers to hands-on experiences. Raise a future paleontologist (古生物学者) with a visit to Penn Dixie where the kids can dig for fossils (化石). Head to East Aurora where learning feels like play at Explore & More Children's Museum.

    Make History

    There's plenty to inspire the imagination of the history lovers in your family on a trip to Buffalo. Appreciate art at the Herschell Carrousel Factory Museum. Pick up a souvenir at the Kazoo Factory Museum or experience life in the 19^th century at the Buffalo Niagara Heritage Village. It's time to make history in Buffalo!