A recent study found people's lives are made shorter in North China. It is showed the life expectancy(平均寿命) had been cut down by 5.5 years there. Researchers（研究者）think that the heavy air pollution in China should be to blame(承担责任). It's really the truth. Our government has already done something. However, it doesn't seem to work so well.

    “Air pollution in China is doing harm to people's health. The harm is much more serious than we can imagine,” said Chen Yuyu of Beijing University, one of researchers of this study.

    Dirty air brings serious problems in North China. In January this year, the air pollution was worse than that in other places. That was caused by rising temperature and waste gas（气体）from coal heating（燃煤）.

    Chinese government should strongly fight with air pollution. They should think of more proper ways to deal with the problem. People should be encouraged to take buses, ride bicycles or walk, instead of driving cars. The factories that pollute heavily should be closed.

    “We need to improve our environment, although it might be expensive. Protecting our environment means protecting ourselves,” Li Hongbin, another researcher of the study said.

    The sun, the moon and the stars are all in the sky. We see the moon and the stars at night. The sun is a ball. It's much bigger than the moon. It gives us heat (热量). The sun has a family. It's the biggest member of the family. The moon is a ball, too, like the sun and the earth. Sometimes it looks as round as a plate (盘子). Sometimes it looks half a plate. It looks bigger because it's much nearer to the earth. It's much smaller than the sun. It's smaller than the stars. The light (光) on the moon comes from the sun. It has no light of its own.

    The stars look smaller than the sun. They look small because they are very far away from us. All day the stars are in the sky. But the light from the sun is too bright. We can't see the stars in the day.

    We each have memory(记忆力).That's why we can still remember things after a long time. Some people have very good memories and they can easily learn many things by heart, but some people can only remember things when they say or do them again and again. Many of the great men of the world have got surprising memories.

    A good memory is a good help in learning a language. Everybody learns his mother language when he is a small child. He hears the sounds, remember them and then he learns to speak. Some children are living with their parents in foreign countries. They can learn two languages as easily as one because they hear, remember and speak two languages every day. In school it is not easy to learn a foreign language because the students have so little time for it, and they are busy with other subjects, too. But your memory will become better and better when you do more and more exercise.

    In 1845, a deadly disease struck the farms of Ireland, killing all the Lumper potato plants. In another place or time, the death of single crop species (物种) might not have been so important. But in Ireland, in 1845, people depended almost solely on the potato for food. The death of one species caused a terrible famine(饥荒). Now, some scientists are worried that such a famine could happen again, but on a much wider scale.

    Over the centuries, farmers have discovered thousands of different species of food crops. Each species has special qualities. Some can be grown in very hot or cold climates. Others are not affected by certain diseases. However, you won't find many of these species in your local supermarket. To feed the seven billion people on Earth, most farmers today are growing only species of plants and farming only species of animals that are easy to produce in large numbers.

    For example, in the Philippines, there were once thousands of varieties of rice: now fewer than 100 are grown there. In China, 90 percent of the wheat varieties grown just a century ago have disappeared. Scientists believe that over the past century, we have allowed more than half of the world's food varieties to disappear.

    One solution to this problem is to collect and store the seeds (种子) as many different plant varieties as we can before they disappear. The idea was first suggested by Russian scientist Nikolay Vavilov. In the 1920s and 1930s, he collected around 400,000 seeds from five contients. More recently, others are continuing the work he began.

    In the U.S. state of Iowa, Diane Ott Whealy wanted to protect historic plant varieties, like the seeds her great –grandfather brought to the U.S. from Germany more than a hundred years ago. She and her husband started a place called Heritage Farm, where people can store and trade seeds.

    More importantly, the people at Heritage Farm don't just store the seeds; they plant them. By doing this, they are reintroducing foods into the marketplace that haven't been grown for years. These food species are not just special in terms of appearance or taste. They also offer farmers food solutions for the future, from the past.

    What is the best way to help control air pollution in our towns and cities? Choose public transportation instead of private cars, or reduce the total amount of cars on the street. These can be useful. But here is a more creative way—write a poem.

    "I write in praise of air. I was six or five, when a magician opened my fist(拳头), and I held in my hand the whole of the sky."

    Professor Tony Ryan (the science expert) and Professor Simon Armitage(the words expert), from the University of Sheffield, UK, came up with the idea.

    But in fact, the poem is not the key part. It is the poster that the poem was written on that plays the biggest part. The poster is 10 meters by 20 meters. It is coated with nanoparticles(纳米粒) of titanium dioxide (二氧化钛). It can absorb the waste from around 20 cars each day if you put it by a busy road. The poster is now displayed on one of the University of Sheffield's buildings.

    It doesn't get rid of all the pollutants from traffic, but it will eat up things called nitrogen oxides (氧化氮). These play a part in breathing problems, including asthma(哮喘).

    The technology is cheap. "It would add less than £100 to the cost of a poster and would turn advertisements into catalysts(催化剂) in more ways than one," Ryan told the BBC.

    He's also working on another idea, which is to add the nanoparticles to washing powder, so that your clothes soak up these poisons while you walk along. And you wouldn't be able to see or feel anything different.