A kind of little cars may take the place of today's big ones many years later. If everyone drives such cars in the future, there will be less pollution in the air. There will also be more space for parking in cities, and the streets will be less crowded.
      The little cars of the future will cost less. Driving will be safer, too, since these little cars can go only 65 kilometers an hour. The cars of the future will be fine for going around a city, but they will not be useful for a long way. Little cars will go 450 kilometers before they need to stop for more gasoline (汽油). If big cars are still used with the small ones, two kinds of roads will be needed in the future. Some roads will be needed for the big, faster cars and other roads will be needed for the small, slower ones.

　　　When you're not at home, many worries may start to crowd your mind. Did I turn the coffee maker off? Did I lock the door? Are the kids doing their homework or watching television? With a smart home, you can quiet all of these worries.

　　　A smart home is a home with a communication network. This network connects devices(装置),such as lights and TV sets, and allows them to be controlled from far away through electrical wiring, mobile phone communication or WiFi over the internet.

　　　More and more people may start to consider owning a smart home, because it makes life much more convenient. It can help keep your room at a certain temperature. It can record what happens inside the home and send the video to your phone. When you are on vacation abroad, you can use a smart home controller to switch on or off the electricity when necessary. Some smart homes can receive a visitor, allowing him to come in and offering him a drink. They can even feed the cat and water the plants.

　　　Besides, smart homes are easy to fix. Most smart home technology and devices are wireless and can be set up with a minimum of tools, using only the guiding information. When a problem appears, you can deal with it yourself without paying a professional.

　　　However, for home-users, the smart home technology is far from perfect. It can be rather expensive to own the technology and the devices. Also, because the smart home system(系统)allow its owner to get home information from anywhere, it leaves the home easy to be attacked by hackers(黑客),who may secretly use or change the information in the system.

　　　Now, many scientists are excited at the future of smart home technology. Imagine being able to get fashion advice from your mirror, or receive food shopping suggestions from your refrigerator. While there are others who worry that those smart devices will make people lazier and lonelier. Whatever it is, one thing is for sure—smart home technology will change the way we live and work.

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    Imagine the situation. You are driving along a desert or on a mountain. You have no idea where you are. You passed the last house two hours ago. Then your car breaks down. It is night and it is cold. You have no mobile phone. What do you do? Well, next time take a GPS with you. This invention may be able to help you. It is a device(装置) which uses satellites (卫星) to find the user's position(位置). It can find your position to within 20 metres. A GPS cannot start your car, but at least you will know where you are.

    GPS, which means Global Positioning System, is a small radio receiver. It looks like a mobile phone. You can hold it in your hand, or put in your pocket. It is sometimes put into a watch or a telephone. We also find GPS devices in cars, planes, or boats. Some of these devices have electronic maps, so you know where you are. For example, in a city they can tell you the name of the street.

    There are three parts to the Global Positioning System. The first part is the receiver. You can hold it in your hand, or have it fixed into your car, plane, etc. The second part is a group of satellites orbiting the Earth. The receiver contacts at least four of the satellites and calculates(计算) its position. The third part of the system is a network of ground stations. They are all over the world. They control the satellites and make sure they are working well.

    Some people think that in the future the GPS will be as common as the mobile. They are becoming cheaper and more and more accurate(精确的). There are also new uses for the GPS. Perhaps they will become like watches. Everyone will have one and you will never be lost again.

    Humans and animals need oxygen to exist. Without it, most living things will die. But where does oxygen come from'? Trees. Trees can take in much carbon dioxide which may be bad for our environment and produce oxygen for us to breathe.

    All people know that trees are important to us. Scientists believe humans cannot live if there are no trees on the Earth.

    Trees are a major source(来源) of food. Apples, oranges, lemons all come from trees.  Humans and animals knew how to get food from trees many years ago.

    In fact, many kinds of important medicine come from trees too. Some special things on trees can be used to produce medicine. Also, trees can make the world beautiful and relaxing. They help protect the soil.