America is the country on the move. In unheard of numbers, people of all ages are exercising their way to better health. According to the latest figures, 59 percent of American adults exercise regularly-up 12 percent from just two years ago and more than double the figure of 25 years ago. Even non-exercisers believe they would be more attractive and confident if they were more active. It's hard not to get the message. The advantages of physical fitness are shown on magazine covers, postage stamps, and television ads for everything from beauty soaps to travel books. Exercise as a part of daily life did not catch on until the late 1960s when research by military doctors began to show the good points of' doing regular physical exercises. Growing publicity(宣传) for races held in American cities helped develop a strong interest in the ancient sport of running. Although running has leveled off in recent years as Americans have discovered equally helpful and sometimes safer-forms of exercise.

    As the popularity of exercise continues to increase, so does scientific evidence(根据) of its health benefits. The key to fitness is exercising the major muscle group strongly enough to almost double the heart rate and keep it doubles for 20 to 30 minutes at a time. Doing such physical exercises three times or more a week will greatly improve physical health in about three months.

    Floods are second only to fire as the most common of all natural disasters.They occur almost everywhere in the world,resulting in widespread damage and even death.Consequently,scientists have long tried to perfect their ability to predict floods.So far,the best that scientists can do is to recognize the potential for flooding in certain conditions. There are a number of conditions,from deep snow on the ground to human error,which cause flooding.

    When deep snow melts it creates a large amount of water.Although deep snow alone rarely causes floods,when it occurs together with heavy rain and sudden warmer weather it can lead to serious flooding.If there is a fast snow melt on top of frozen or very wet ground,flooding is more likely to occur than when the ground is not frozen.Frozen ground or ground that is very wet cannot absorb the additional water created by the melting snow.Melting snow also contributes to high water levels in rivers and streams.

    Rivers that are covered in ice can also lead to flooding.When ice begins to melt,the surface of the ice cracks and breaks into large pieces.These pieces of ice move and float down the river,They can form a dam in the river,causing the water behind the dam to rise and flood the land upstream.If the dam breaks suddenly,then the large amount of water held behind the dam can flood the areas downstream too.

    Broken ice dams are not the only dam problems that can cause flooding.When a large human-made dam breaks or fails to hold the water collected behind it,the results can be devastating.Dams contain such huge amounts of water behind them that when sudden breaks occur,the great force of the water is like a great tidal wave.The dam waters can travel tens of kilometres,cover the ground in metres of mud and litter,and drown and crush every thing and creature in their path.

    Although scientists cannot always predict exactly when floods will occur,they do know a great deal about when floods are probably going to occur.Deep snow,ice-covered rivers,and weak dams are all strong conditions for potential flooding.

    In modern society, it is usually considered good to be an extroverted(外向的) person. This means that life can be hard for introverted people. Their talents and abilities are often not recognized.

    Some people often try to make introverts more outgoing. They think that being an introvert is a problem. But there is nothing wrong about being an introvert. Introverts are not necessarily afraid of meeting and talking to others. They simply prefer to spend time on their own, away from the crowds. They like reading, writing and taking walks in the countryside. But extroverts need other people. If they spend a lot of time on their own, they get bored. They tend to be impulsive and talk a lot.

    Our society puts a lot of pressure on people to be extrovert, to be outgoing and self-confident on every occasion. Susan Cain, the author of the book Quiet: The Power of Introverts in a World That Can't Stop Talking, has spoken about this problem. "I was nine years old," Cain says. "In my suitcase there were lots of books. This seemed normal to me, because in our family we always read a lot. I thought it would be the same at summer camp. But I was wrong. To create camp spirit, all the children had to sing a cheer every morning. I couldn't understand why. In the evening, I took out a book from my suitcase. But another girl said, 'why are you being so quiet?' The second time I took out a book, the counselor(辅导员) came to see me. She told me to remember the camp spirit and that it was important to be outgoing."

    At work, extroverts often do well. At job interviews, it is usually good to appear extrovert. It suggests that you will be good at the job. But it is wrong to think that only extroverts are good leaders. Introverts work in different ways to extroverts, but they can still do really great things. Darwin, for example, was a quiet, family man. He often took long walks so that he could think clearly. But Darwin's ideas about evolution were revolutionary.

    Introverts must understand that it is perfectly okay to be the way they are. It is not necessary to want to be the center of attention. You don't have to take part in noisy, social activities if you don't want to. And it is not necessary to try to become more outgoing.

    The islands of Malta and Gozo are brilliant for a family holiday, packed with fun places to visit whatever your children's ages. The islands' small size means everywhere is within easy reach.

    Sandy beaches and swimming spots

    One of Malta's best beaches for families is soft-sanded, sheltered Golden Bay. Older children can try activities such as stand-up paddle boarding, sailing or windsurfing, while the gentle slope of the beach makes it easy for younger kids to safely paddle in the sea.

    Eating out

    Children are welcome at most restaurants, though more upmarket places often only accept older kids. There are often kids' menus that tend to offer pizza, but you can always ask for a half portion of a starter dish (portions are huge in Maltese restaurants). With a wide range of cuisines on offer, children are bound to find something they'll like, Maltese food is strongly influenced by Italian cuisine, so there's pizza and pasta galore, and some kids will love the national dish-fried rabbit

    Accommodation

    Try to schedule at least a few days on Gozo as there are lots of self-catering farmhouses with pools to rent and it's even easier to get around than Malta. Smaller hotels in Valletta usually only accept older children.

    Transport and other tips

    The easiest way to get around Malta and Gozo is to drive, but the local bus service is reliable, easy to use, and fairly inexpensive. Buses are frequent between major towns, but only roughly hourly to and from smaller places. Ferries run between Malta and Gozo, and you can take tourist boats over to Comino.

    Hacking isn't just for computers and smart phones. According to a study, scientists have found a way to hack a plant's genes in order to make it use sunlight more quickly. Someday, the results could increase the number of food produced around the world.

    Scientists used tobacco plants in the study because it is easy to change the plants^' genes. Hacked plants are larger than normal plants.

    Photosynthesis is the word used to describe how plants use sunlight, water and carbon dioxide to make their own food. Scientists say this is a very slow process. Plants use less than 1 percent of the energy. But by hacking a plant's genes, the scientists were able to increase the amount of leaf growth on plants between 14 and 20 percent. Scientists hacked the plant's protective system. Normally, this system starts when a plant gets too much sunlight. When the plant senses the light, it creates more leaves. When the plant is in shade, the protective system is turned off. But the process is slow.

    The new study sped up the process by changing the plant's genes, the protective system turned on and off more quickly than normal. As a result, leaf growth on the plants scientists used in the study increased. Leaf growth on two plants increased by 20 percent, while leaf growth on a third plant increased by 14 percent. Scientists conducted the study on tobacco plants. But they think the genetic changes would produce the same results in corn and rice.

    Agriculture professor Tala Awanda said the study makes sense, but cautioned the yield（产量）might not be quite so high for conventional food crops. Still, she added in an email, "this study remains a breakthrough,"

What better way to experience the history of a site than to have a hand in actually preserving it? This was the thought behind the founding of Adventures in Preservation (AIP) in 2001. The nonprofit's founders. Judith Broeker and Jamie Donahoe, were both long time preservationists and world travelers. They had seen a great many buildings in poor condition, as well as buildings that had been "restored" without the benefit of conservation expertise.

Twelve years on, they are still involved in the day-to-day management of the organization, supported by a volunteer staff located around the world, Judith's favorite projects have long been the ones in Eastern Europe, and she enjoys opportunity to travel there each year. She, along with anyone else who's joined an adventure, always quotes their fellow jammers, as they're called, as the highlight of each project. The groups are made up of people from all different ages, occupations, and cultures. Yet each time, they form a strong bond and work so well together that the work becomes fun. Which, after all, is the point of a working vacation, no?

Raising understanding of people's own heritage(遗迹) is another part of AIP projects. In many places, there is so much focus on the news that not only are heritage buildings being lost but so are the traditional building skills needed to keep them. By providing training and raising awareness of the importance of their heritage, AIP is helping keep both alive.

Next year, AIP has projects in Europe and the US. There will be even more projects the following year as projects currently under development in Ghana, Armenia, Ukraine and the US come on line. Each project is also an opportunity for travel, adventure, and personal growth, and AIP welcomes people from around the world to join a project and" "jam" with them.