Language students often think they have memory problems. They worry because they can't remember words. In fact, the problem usually isn't with their memory. The problem is with how they study.

    To remember words better, you need to understand how memory works. There are two kinds of memories: short-term and long-term. When you see, hear, or read something, it goes first into short-term memory. But short-term memory lasts for only a few seconds. You will only remember something longer if it goes into long-term memory. Your long-term memory is like a very big library with many, many books. And like a library, it's organized (有条理的). When you put away a book – or memory – you can't just leave it anywhere. You have to choose a place where you can find it again.

    How can you do this with vocabulary? The answer is to work with the word and think about the word in new ways. You can do this by writing new sentences that include it. Even better, you can invent a little story about the word, with people or places that you know. Another way is to make a picture in your mind with the word. For example, if the word is height, you can think of the tallest person you know and try to guess his or her height. All of these activities are good ways to think about words. They make the meaning of words stronger in your long-term memory. And they give a way to find a word when you need it.

    Today, nearly five hundred weather stations in sixty countries receive satellite pictures.  When they receive new pictures, the meteorologists compare（比较）them with earlier ones.  Perhaps they may find that the clouds have changed during the last few hours.  This may mean that the weather on the ground may soon change, too.  In their next weather forecast, the meteorologists can say this.
　 So the weather satellites are a great help to the meteorologists.  Before satellites were invented, the scientists could forecast the weather for about 24 or 48 hours.  Now they can make good forecasts for three or five days.  Soon, perhaps, they may be able to forecast the weather for a week or more ahead（提前）.

    Rubbish is a major kind of environmental pollution. Each person produces about 2kg of rubbish a day. We are making waste products faster than nature can break them down. And we are using up resources(资源)faster than they can he replaced(取代).

    This adds up to trouble for the environment. Where does all that rubbish go? What can be done to help dispose of(处理)rubbish? How can we make less rubbish?

    Rubbish isn't just the smelly rotting fruits, vegetables or meat that we throw away(抛弃) in our homes Those are only a small part of all tile stuff we throw away. We create other kinds of waste, in construction, mining and in our factories.

    Did you ever wonder what happens to your rubbish? Most is burned(燃烧)or buried in landfills(垃圾填埋场). Less than a quarter of our waste is recycled(回收).

    With a population of 1.3 billion(十亿), rubbish is a big problem for China. Chinese city create around 148 million tons of rubbish every year. The amount is growing at around 10 percent each year.

    Once we used about 3 billion plastic shopping bags everyday in China. The result was a great waste of resources and serious pollution. So we did something about that. Now we use more cloth bags and shopping baskets when we shop.

    In the coming years China will build waste-to-energy plants in cities to clean up the rubbish. But there's a lot more that needs to be done. And you can play a role.

    The monarch is one of the most beautiful butterflies. It is famous for its yearly migration（迁徙）from the northern part of North America to Mexico, There, millions of monarchs spend the winter together in one small area. This migration is one of the greatest wonders of nature. Yet this behavior has now put the monarch at risk.

    Every September, millions of monarchs from the United States fly to Mexico. After about two months of flying time, they reach their sanctuary(庇护所)in central Mexico. Then, in the warm climate of private and quiet valleys, far from most human activity, the butterflies create one of nature's great scenes. They cover every tree with bright color. The show lasts until spring, when the butterflies return north.

    While they are all crowded together, the monarchs are highly weak. If the environment in those valleys was disturbed, the whole species could be hurt or even die out. That is why for many years scientists who knew about the monarchs' winter sanctuary kept the location a secret.

    In recent years, however, the monarchs' secret has been discovered. Today, the butterflies' winter sanctuary is crowded with tourists, who disturb the environment. Worse still, local farmers who need more land to farm have begun to take up the area. They are cutting down trees, making it difficult for the butterflies to survive. They should not farm in the monarchs' sanctuary.

    People should act immediately to protect the species' winter sanctuary. Local farmers must be helped so that they no longer need to take land from the butterflies. Tourist visits to the butterflies' hidden valleys must also be limited. Unless these steps are taken soon, in a few years the monarch butterfly of North America may be just a beautiful memory.

    Many scientists think that the Earth is getting warmer and warmer. If the change continues, the natural world and human society will face danger. Scientists believe human activity is responsible for the climate change. We produce too many greenhouse gases. They keep heat in the air and make the Earth warm.

    Many of the world's governments agree. And they want to solve the problem. So from 7 to 18 December, 2009，they held a conference in Copenhagen, Denmark to talk about global warming and climate change.

    Representatives(代表) from 192 countries and regions went to the meeting. Although they have not reached an agreement, the Copenhagen Accord(《哥本哈根协议》) was an important beginning to save the Earth. It was made by a small group of countries including China，the USA，India, Brazil and South Africa. Some other countries at the conference also showed support.

    What are the key points of the Copenhagen Accord? The accord limits global temperature increases to 2C by 2050. Scientists think it could help the world to avoid serious climate change.

    The accord also says that developed countries must promise to cut greenhouse gas emissions(排放) to the UN by 31 January, 2010. The accord asks developed countries to give money to help developing countries.

    Many countries and organizations are disappointed that the conference didn't reach a legal document(法律文书). And they think the accord is not clear enough about its goals.

African leaders are worried that the goal of a 2℃ global temperature increase isn't good enough, because it will mean a much higher increase in temperature across Africa. This could cause big problems like food and water shortages across the continent.

    Still, UN Secretary General believes the conference was an "improvement".

    "Finally we reached a deal," Ban said," the accord may not be everything everyone had hoped for, but this is an important beginning."