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 human brain weighs about 1.4 kilograms, but it can hold much more information than most computers．However, there is another difference between humans and computers．Computers don't forget information they are given, but humans often do．No one remembers everything, and luckily we don't usually have to．But everyone can improve their memory if they want to．Here are some suggestions．

    Try to use new information immediately．For example, if you meet someone who says "Hi! I'm Carlos．"Don't just say "Hello．" Repeat the person's name．Say "________"

    Break a big number into smaller parts． For example, it's hard to memorize (记忆) 109244153．But if you break it into three parts  109/244/153--it becomes easier．

    Write out what you need to remember over and over again．This will help you keep it in mind longer, especially for memorizing formulas (公式) or facts．

Always review information．If you bring what you've learned back to your mind, it becomes easier to remember． For example, before you go to sleep, it's a good idea to review the new things you learned that day．

    Discuss with a friend．It is always easier to remember things through discussions．You can have a discussion about what's right and what's wrong, and it will lead to the right answer．

    Never tell yourself that you have a bad memory．You can always do something to help improve your memory．And everyone's memory gets better if they use it often enough．

    All the suggestions are helpful．If you follow them, you are certain to improve your memory．

    If you travel by air across the center of Africa or South America, you fly over forests for thousands of kilometres．These great forests are the seas of trees．They are full of thousands and thousands of different kinds of plants and animals．However, the world's forests are getting smaller all the time．We are cutting down the trees because we need wood, and we need more farmland as well．Some people say that there will not be any forests like these left in 20 to 30 years．What will happen if they disappear? If we cut down our forests, a lot of plants and animals will disappear from the world, in a lot of places the new farmland will soon look like the old deserts, for example, crops will not grow there．What's worse, it will not rain very often, and the weather will get very hot．Perhaps the climate of the world will change, which will be dangerous for everyone in the world．That is why we must take care of our forests．