All too often, a choice that seems sustainable(可持续的)turns out on closer examination to be problematic. Probably the best example is the rush to produce ethanol(乙醇) for fuel from corn. Corn is a renewable resource —you can harvest it and grow more, almost limitlessly. So replacing gas with corn ethanol seems like a great idea. 

    One might get a bit more energy out of the ethanol than that used to make it, which could still make ethanol more sustainable than gas generally, but that's not the end of the problem. Using corn to make ethanol means less corn is left to feed animals and people, which drives up the cost of food. That result leads to turning the fallow land –including, in some cases, rain forest in places such as Brazil—into farmland, which in turn gives off lots of carbon dioxide (CO) into the air. Finally, over many years, the energy benefit from burning ethanol would make up for the forest loss. But by then, climate change would have progressed so far that it might not help.

    You cannot really declare any practice “sustainable” until you have done a complete life-cycle analysis of its environmental(环境的) costs. Even then, technology and public keep developing, and that development can lead to unforeseen and undesired results. The admirable goal of living sustainably requires plenty of thought on an ongoing basis.

    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.

    More than two thirds of the world's polar bears will be wiped out by 2050, according to a shocking new study. By then, scientists say, global warming will have melted 42 percent of the Arctic sea ice. By 2100, only a very few of these important creatures will be left.

    The report has been produced by the US Geological Survey. The scientists have publicized their findings in the hope of influencing US Interior Secretary Dirk Kempthorne, who has been asked to put polar bears on the US endangered species list.

    Polar bears depend on floating sea ice as a platform for hunting seals, which are their main food. Without enough ice, polar bears would be forced to go onto the land, where they are poorly skilled hunters, and would be unlikely to adapt to the life on the land in time. Experts say few little bears would survive and the stress could make many females unable to get pregnant.

    The team of American and Canadian scientists spent six months studying bears, on the ground, from spotter planes and in the lab, using computer models. Some team members fear the result is even worse for the bears than what their report says. They say the Arctic is warming faster than anywhere in the world and much faster than their computer had been forecasting. Satellite observations have showed that the ice has decreased to an all­time low.

    However, not everyone in the scientific community believes that global warming is happening on such an alarming scale. Another investigation has found that polar bears are still being hunted by wealthy “sportsmen” who want their skins and heads. At least ten international companies offer bear­hunting trips.

    In the kitchen of my mother's houses there has always been a wooden stand (木架)with a small notepad(记事本)and a hole for a pencil.

    I'm looking for paper on which to note down the name of a book I am recommending to my mother. Over forty years since my earliest memories of the kitchen pad and pencil, five houses later, the current paper and pencil look the same as they always did. Surely it can't be the same pencil. The pad is more modern, but the wooden stand is definitely the original one.

    "I'm just amazed you still have the same stand for holding the pad and pencil after all these year." I say to her, walking back into the living-room with a sheet of paper and the pencil. "You still use a pencil. Can't you afford a pen?"

    My mother replies a little sharply. "It works perfectly well. I've always kept the stand in the kitchen. I never knew when I might want to note down an idea, and I was always in the kitchen in those days."

    Immediately I can picture her, hair wild, blue housecoat covered in flour, a wooden spoon in one hand, the pencil in the other, her mouth moving silently. My mother smiles and says, "One day I was cooking and watching baby Pauline, and I had a brilliant thought, but the stand was empty. One of the children must have taken the paper. So I just picked up the breadboard and wrote it all down on the back. It turned out to be a real breakthrough for solving the mathematical problem I was working on."

    This story—which happened before I was born—reminds me how extraordinary my mother was, and is, as a gifted mathematician. I feel embarrassed that I complain about not having enough child-free time to work. Later, when my mother is in the bathroom, I go into her kitchen and turn over the breadboards. Sure enough, on the back of the smallest one, are some penciled marks I recognize as mathematics. Those symbols have traveled unaffected through fifty years, rooted in the soil of a cheap wooden breadboard, invisible(看不到的)exhibits at every meal.

    A picture speaks a thousand words. And with over a thousand emoji pictures to represent our words, who needs to speak or write any more? According to Professor Vyv Evans of Bangor University, emoji is the UK's fastest-growing language in history. These little electronic pictures started life in Japanese mobile phones in the 1990s and are now hugely popular. They have inspired fashion, like the real-life dress copied from the dancing lady emoji, and are even recognized as art! In New York's Museum of Modern Art you can now see the first set of the 176 original emojis.

    Why do we love them so much? They allow us to personalize text and have fun as we express ourselves, make people laugh and be creative in how we use them. UK teenagers also told us they really appreciated the fact that emojis are quick and easy.

    People have their favourite emojis. In the UK, the most used emojis are ' face with tears ofjoy', ' face blowing a kiss' and 'Iove heart'. Maybe (with emojis at least) the British are more fun and romantic than people think! Companies such as McDonalds have also tried to use people's love of emojis to make advertisement. They used a series of emojis to tell a story of a disappointing day given a happy ending by a visit to McDonalds. Unluckily for McDonalds, most people added the vomiting(呕吐) emoji to the blank space after the story.

    What is the future of emoji? Is emoji developing so rapidly that it will soon compete with English as a global language? Or is technology changing so fast that emoji will soon be forgotten when the next big thing comes along? It is hard to say and even technology and language experts are divided on the subject.

    What do you think? Keep your eyes open for new developments!

    It's school time again! You're probably feeling excited and maybe a little sad for the vacation is over. Some kids feel nervous on the first day of school because of all the new things: new teachers, new friends, and maybe even a new school. Luckily, these "new" worries only stick around for a little while. Let's find out more about going back to school.

    Most teachers kick off the school year by introducing themselves and talking about what you'll be doing that year. Some teachers give students a chance to tell something about themselves to the rest of the class.

    When teachers do the talking on the first day, they often go over classroom rules so you'll know what's allowed and what's not. Pay close attention so you'll know if you need to raise your hand to ask a question and what the rules are about visiting the restroom.

    You might already know a lot of people in your class on the first day. But it's a great day to make new friends, so try to say "hello" to the kids you know and new ones that you don't. Make the first move and you'll be glad about what you did and so will your new friends!

    Most teachers let you pick your own seat on the first day, but by the second or third morning, they'll have mapped out a seating plan. It's a good idea to write down where your seat is in your notebook so you don't forget.

    Here are a few final tips for a fantastic(奇异的) first day: Get enough sleep. Have a healthy breakfast. Try your best. Develop good work habits, like writing down your assignments(作业) and handing in your homework on time. Take your time with schoolwork. If you don't understand something, ask the teacher.