Do you ever wonder why trees begin to bud (发芽) earlier in some cities? Scientists finally found the answer but it's not very pleasant. New science suggests a relationship between light pollution and the timing when trees produce buds, which signals the arrival of the spring season.

    Light pollution is defined by the Lighting Research Center as the unwanted consequence of outdoor lighting such as street lights. Excessive (过多的) man-made light at night results in disturbed natural cycles, and also prevents the observation of stars and planets at night. But its effect on the environment goes beyond that.

    By studying some trees, researchers found out that trees that are more exposed to artificial lighting at night bud up to 7.5 days earlier than those at the natural nighttime setting. And they found out that light had a more significant effect than temperature when the buds came out. The early budding may cause problems for insects, which feed on leaves, and the birds which then feed on them in turn. Professor Richard Ffrench-Constant, who helped lead the research, explained that more than the budding of trees, the study implies the danger to the balance of the ecosystem. “At the moment, caterpillars (毛毛虫) are timed to hatch to make the most of the opportunities to feed on freshly budded leaves, and birds hatch in time to feed on the young caterpillar,” he said.

    Migratory (迁徙的) birds are also negatively affected by light pollution. The glare might confuse them and make them lose their flying sense. The phenomenon might explain why some birds accidentally knock into buildings.

    Such results stress the need to pursue studies that aim to measure the effect of light pollution. If the issue were left to continue, it is estimated that by 2100, spring would begin almost a full month earlier than it does today.

    If you need glasses to read this, you are among the majority of Chinese students. That's because most students in China are short-sighted which means they can only see things close up and distant things will be blurry. Four-fifths of high school students wear glasses and now more and more children in primary school need glasses, too.

    This epidemic of poor eyesight has two very simple causes: too much time spent indoors studying and too little time spent outdoors playing. Reading and writing for hours and hours, sometimes in poorly lighted rooms, causes eyesight to weaken. But students have to do this because there is so much pressure on them to succeed in school. And because they spend so much time indoors at school and at home, they have less time to spend outdoors enjoying the sun.

    The sun, as a consequence, is important in developing good eyesight. Exposure to daylight releases a chemical in the eyes that prevents, or at least delays, short-sightedness. According to a study by Ian Morgan of Australian National University, Australian children and Chinese children have the same level of eyesight before they start school, but once they enter primary school, Chinese children only spend about an hour a day outside, while Australian children spend three to four hours each day in the sunshine. The result is that while about 40 percent of Chinese primary school students need glasses, only three percent of Australian children do.

    Wearing glasses may not seem like a big deal. For some, wearing glasses can even be an opportunity to make a fashion statement. But poor eyesight at a young age can have serious long term consequences. As you get older, your eyesight can worsen and lead to things like macular degeneration(黄斑变性), a condition of the eyes for which there is no cure and which can eventually lead to blindness.

    With all that in mind, don't you think it's time to give your eyes a break? Try spending a little less time inside and go for a walk in the park, instead. It's the healthy thing to do and your eyes will thank you for it.

    Grown-ups are often surprised by how well they remember something they learned as children but have never practiced ever since. A man who has not had a chance to go swimming for years can still swim as well as ever when he gets back in the water. He can get on a bicycle after many years and still ride away. He can play catch and hit a ball as well as his son. A mother who has not thought about the words for years can teach her daughter the poem that begins "Twinkle, twinkle, little star" or remember the story of Cinderella or Goldilocks and the Three Bears.

    One explanation is the law of overlearning, which can be stated as follows: Once we have learned something, additional learning trials increase the length of time we will remember it.

    In childhood we usually continue to practice such skills as swimming, bicycle riding, and playing baseball long after we have learned them. We continue to listen to and remind ourselves of words such as "Twinkle, twinkle, little star" and childhood tales such as Cinderella and Goldilocks. We not only learn but overlearn.

    The multiplication tables(乘法口诀表) are an exception to the general rule that we forget rather quickly the things that we learn in school, because they are another of the things we overlearn in childhood. The law of overlearning explains why cramming (突击学习) for an examination, though it may result in a passing grade, is not a satisfactory way to learn a college course. By cramming, a student may learn the subject well enough to get by on the examination, but he is likely soon to forget almost everything he learned. A little overlearning, on the other hand, is really necessary for one's future development.

    If you are interested in studying at an American university, you have to take the Test of English as a Foreign Language. The test is widely known as the TOEFL. It is the most widely used language exam for American universities.

    There are two major kinds of the TOEFL test. The first is the IBT，or Internet based Test. It is offered in most of the world and accepted by nearly every university and scholarship program in the United States. The other kind of the test is called the Paper­based Test or PBT. The PBT is less costly to take and does not require use of the Internet.

    But how to get started with TOEFL? Here are some tips.

    ⒈Plan ahead — It takes a long time to improve your TOEFL score. Do not expect a big lift in your test results after two weeks. You will have to spend a lot of time and energy.

    ⒉Master the basics first — You should have to be good at basic English before you take the test. If you score below 500 on the PBT or 70 on the IBT, study for a few months and come back to the TOEFL later.

    ⒊Get a study guide — It is easy to find study guides for the IBT. Pearson, Barron's, ETS, and Kaplan all produce quality materials, take a practice test once or twice a month. The best study guides will have explanations in the answer key.

    ⒋Use outside resources — Remember, you are learning a language, not a test. You can improve your TOEFL score by making English part of your daily life. Some simple ways are listening to English speakers, watching movies and reading newspapers. Some others are reading English textbooks, sending and reading text messages in English, and writing online in English.

    The best way to do well on the TOEFL is to know English well. The real goal of the test is to measure how well a student can communicate in English­speaking classroom.

    If you want to know more, please click here.

    The meaning of the word "volunteer" may be a little different in different countries, but it usually means "one who offers his or her services". There are many different ways in which people can volunteer, such as taking care of sick people, working in homes for homeless children, and picking up garbage from beaches and parks. Volunteers may work within their own countries or in other countries. They are often people with a strong wish to help those who are less fortunate than themselves. Volunteer don't expect any kind of pay.

    At the root of volunteering is the idea that one person may have the ability to offer services that can help other people. Tracy, a good friend of mine, however, recently came back from India with a new idea of what being a volunteer means. She worked for two and a half weeks in one of Mother Teresa's homes in Calcutta. The following is her story.

    "I first heard about Mother Teresa in my high school. We watched a video about her work in India and all over the world. I was so moved by her spirit to help others and her endless love for every human being that after I graduated from high school, I also wanted to try her kind of work. So with two friends, I flew to Caltutta for a few weeks."

    "I was asked to work in a home for sick people. I helped wash clothes and sheets and passed out lunch. I also fed the people who were too weak to feed themselves and tried to cheer them up. I felt it was better to share with them than to think that I have helped them. To be honest, I don't think I was helping very much. It was then that I realized that I had not really come to help, but to learn about and experience another culture that helped improve my own understanding of life and the world."

    People like to post their selfies(自拍照) on social media. To know more about it, scientists at Syracuse University in New York recently did a research and came up with some surprising findings.

    People who post selfies and use editing software to make themselves look better show behavior connected to narcissism(自恋), the researchers said. Makana Chock, a professor from Syracuse University, said because social media is mostly used by people to share unimportant information about their lives, it is a good place for people to "work towards satisfying their own vanity." Those "likes" under their Facebook selfies make them feel good.

    Besides, people who post group selfies show a need for popularity and a need to belong to a group, the research found. Some people feel "peer(同伴) pressure" to post selfies and some follow the popular belief that if there is no picture of an event or experience, it did not really happen. "Anyway, it shouldn't be seen as negative. People get sense of satisfaction especially when they get likes. And it does no harm," Chock said.

    Other findings from the study include: There are no major differences on how often men and women post selfies and how often they use editing software. But men who post selfies showed more of a need to be seen as popular than women who posted selfies.

Chock said posting selfies on social media is not all that different from what people have done for many years. On trips and special events, our parents and grandparents used cameras instead of phones to take photos. They would bring back photos to show friends and family. You had no choice but to look at them. You probably commented about how nice everyone in the photos looked, especially children and the person showing the photos. They were happy to hear your comments. That was the old way of "clicking like". On social media, however, people can decide not to look at photos — even if they click "like".