Some materials are obtained from natural resources that are changed by chemical processes in a laboratory. The resulting artificial materials are synthetic, or human-made.

    Plastic is a synthetic substance, obtained from petroleum, a fossil fuel. The molecules（分子）in petroleum are split and then linked into chains. Plastic is an example of a polymer, a material made of repeating patterns of atoms linked together. Most polymers are synthetic. They are made by polymerization, the process of chemically linking many smaller molecules to form a larger molecule that has different physical features. Some polymers, such as proteins, occur naturally.

    Plastic is a key component of many products. When heated into an almost-liquid form, plastic can be made into fibers, sheets, or molds（模具）. It can be mixed with other elements to remain flexible, or it can harden into a solid. Plastic fibers can be made into clothing or carpeting. Sheets of plastic can be made into plates. Molded plastic can be sued for protective helmets or car bumpers.

    Most plastics can be reheated and remolded repeatedly. This feature makes plastic very easy to use. Polymers can be pulled into fine strings or molded into almost any kind of shape. For example, tubes of plastic can be shaped into bottles by different processes. One such process is extrusion blow-molding. Most plastics are also resistant to many chemicals that might harm other materials. This quality is the reason that so many cleaning liquids are packaged in plastic bottles.

    Plastics are good insulators that can stop electricity or heat to pass through. Look around your kitchen, and observe where plastics are used. Pot handles are sometimes made of plastic, as are cooking tools, toaster controls, and microwave cookware. Food-storage wraps and containers may be made of plastic. Take a walk outdoors, and note all the plastic items you see. Gardening tools, such as watering cans and sprayers, are often made of plastic. Swings and slides made of plastic do not become as hot as metal, so they are safer for play. Because plastics can be heated, remolded, and made into something else, they can be recycled and reused.

    No rows of desks in this classroom, and no teacher lecturing at the front. In fact, that's something Barrie teacher Liz Collett rarely does. Instead, she's on the move, talking to students about their work, from the small group sitting on the floor playing games to others nearby figuring out a math problem.

    The children in this class do not take a spelling test all year－in fact, the school avoids all pencil-and-paper tests－nor do they get assigned homework. Instead, their teacher gives them immediate feedback（反馈）on their work throughout the day.

    Welcome to the school of the 21st century, a place where teachers and students cooperate all the time. Such advanced classrooms are trying things, which some might consider as coddling kids－letting students give a voice-recorded essay instead of a written one or even allowing teens to design their own courses.

    Though some people blame（谴责）schools for dumbing things down（降低教育标准）, others will say such changes are actually based on the newest research on how to attract today's youth and increase not only their interests, but also their achievements. Many of today's school are not holding kid's interests. And if they Ye not interested, they're not learning－and isn't that the point?

“Students today say they want their education to be useful and valuable, and don't want it to be simply repeating the facts. That's the kind of learning that be happening for many kids,” says Penny Milton, a researcher. “What we could argue is that to become good learners, they need to become thinkers.”

    Jan Olson, anther researcher, says schools have been operating the same way since the Industrial Revolution. But the digital age is bringing an education revolution. While using technology is a part of it, what's important for students is being able to use information and understand it, not just remembering it.

    Today's learner needs fewer traditional tests and more “effective” feedback, ongoing discussion with a teacher, which studies have found is the number one factor in improving achievement.

    If you do not use your arms or your legs for some time, they become weak. When you start using them again, they slowly become strong again. Everybody knows that. Yet many people do not seem to know that memory works in the same way.

    When someone says that he has a good memory, he really means that he keeps his memory in practice by using it. When someone else says that his memory is poor, he really means that he does not give it enough chance to become strong.

    If a friend says that his arms and legs are weak, we know that it is his own fault. But if he tells us that he has a poor memory, many of us think that his parents are to be blamed(责备), and few of us know that it is just his own fault.

    Have you ever found that some people can't read or write but usually they have better memories? This is because they cannot read or write and they have to remember things; they cannot write them down in a little notebook. They have to remember days, names, songs and stories; so their memory is the whole time being exercised. So if you want to have a good memory, learn from the people: practice remembering.

    We Brits love the idea of a real Christmas tree but not so many of us like the realities of dragging (拖拽) a 7ft Norway Spruce through the house and leaving needles all over the place.

    If you count yourself among the reluctant group, then it may be time to go fake (假的) . After all, buying an artificial Christmas tree needn't mean accepting defeat. There's a huge range of choices and sizes, including pre-lit trees, which will save you the frustration of trying to string your own lights.

    Another big advantage of choosing an artificial Christmas tree is cost: artificial trees can last for decades, so they work out cheaper than paying for a real tree every year. Like now retailers (零售商) are offering great deals at the moment: at Tesco, there's 25 percent off artificial Christmas trees. Meanwhile, you can take advantage of the current 3 for 2 offer at Argos to fill your house with not one, not two, but three. You may perhaps partner up with friends who are also looking to invest.

    Of course, keep your tree for years and years and it will start to pay you back in terms of carbon footprint; however, a “real” one will always have to be transported, used and dealt with every year.

    Are there any downsides? Yes. You might think you're saving the planet, but a fake tree is actually not an environmentally friendly option. Most are made in factories in Asia, resulting in some serious air miles to reach the UK. They're made from metal and plastic, and many end their lives in landfill (垃圾填埋).

    Another problem with a fake tree is that they don't look very natural and of course you won't get that lovely pine smell either. You'll also need to find space for storage.

    One of the latest trends（趋势） in American Childcare is Chinese au pairs. Au Pair in Stamford, Conn, for example, has got increasing numbers of request for Chinese au pairs from aero to around 4, 000 since 2004. And that's true all across the country.

    "I thought it would be useful for him to learn Chinese at an early age" Joseph Stocke, the managing director of a company, says of his 2-year old son. "I would at least like to give him the chance to use the language in the future, " After only six months of being cared by 25-year-old woman from China, the boy can already understand basic Chinese daily expressions, his dad says.

    Li Drake, a Chinese native raising two children in Minnesota with an American husband, had another reason for looking for an au pair from China. She didn't want her children to miss out on their roots. " Because I am Chinese, my husband and I wanted the children to keep exposed to(接触) the language and culture." she says.

    "Staying with a native speaker is better for children than simply sitting in a classroom," says Suzanne Flynn, a professor in language education of Children. "But parents must understand that just one year with au pair is unlikely to produce wonders. Complete mastery demands continued learning until the age of 10 or 12. "

    The popularity if au pairs from China has been strengthened by the increasing numbers of American parents who want their children who want their children to learn Chinese. It is expected that American demand for au pairs will continue to rise in the next few years.

    The koala is an unusual creature. Native to Australia and a bit bigger than a rabbit, it spends most of its time in eucalyptus trees（桉树）, feeding on leaves that are poisonous to nearly every other animal on the planet.

    The koala sleeps about 22 hours a day and spends the remainder of its time eating and resting. It might spend 10 minutes a day moving, experts say, usually from one tree to another. It has a soft pad at the end of its spine and extra thick fur on its rear end to make the effort, of sitting more comfortable.

    Threats and protective measures

    The unique lifestyle of the koala has helped it prosper, but today the cute and iconic creature is facing threats from habitat loss, disease and a changing climate. Koala populations are expected to decline by 50 percent in the next 20 years according to the Australian Museum.

    To help protect these animals, which bring in an estimated $1.1 billion to Australia each year through koala-related tourism, an international team of researchers has published the first complete genome（基因组）of the koala. Their hope is that the keys to the marsupial's（有袋动物）long-term survival might be planted in its genetic code.

"The ultimate goal is that we won't have to…rescue them from the edge of extinction," said Rebecca Johnson of the Australian Museum Research Institute in Sydney, who led the work.

    "Now we have a really good understanding of the koala genome, and we are in a fantastic position to use that knowledge to help us manage them."

    Early findings

    An elementary analysis of the koala's genome, published in Nature Genetics, has already yielded some interesting findings.

    For example, the authors found that, compared to other mammals, the koala's DNA includes an expansion in the number of genes that encode for enzymes involved in anti-poison. That allows them to have a diet that depends almost entirely on eucalyplus leaves which are unusually high in poison. However, it also means that koalas metabolize（代谢）medicines like anti-chlamydia antibiotics faster than other animals.

    The koala genome also revealed why koalas are such famously picky eaters. They are known to consume leaves from just 20 of Australia's 60 known eucalyplus species. And even when they are in one of their preferred trees, koalas take leaf selection very seriously.

    Information waiting to be discovered

    Johnson said that the information encoded in the koala's DNA is already being included in management strategies by conservation groups. However, she said the findings described in the new paper represent the early stages of what can be gleamed from the marsupial's genome.

    "The data is public, and I would love for anyone to start mining it and see what other amazing things they can find," she said." Once you have a genome of this quality, the sky's the limit with what you can do with it."