There is little rain in desert. Because deserts are so dry, they have no "quilt" to help stop the soil from going away. As a result, they may get very hot during the day with the sun shining, but don't hold the heat overnight. Many deserts can quickly get cold once the sun goes down. Some deserts can reach temperatures of over 100 degrees F during the day and then drop below freezing (32 degrees F) during the night.

The largest hot and dry desert in the world is the Sahara Desert in Northern Africa. The Sahara is a sandy desert with great sand hills. It covers over 3 million square miles of Africa. Other large deserts include the Arabian Desert in the Middle East, the Gobi Desert in Northern China and Mongolia, and Kalahari Desert in Africa.

Animals that live in the desert are also used to needing little water. Many get all the water they need from the food they eat. Other animals keep water that they can use later. The camel stores up fat in its hump while other animals keep something they need in their tails.

Only certain types of plants can live in the terrible environment of the desert. You won't see a lot of tall trees in the desert. Most plants have a way to keep water in their leaves, or trunks so they can live a long time without water.

Now deserts cover around 20% of the world's land, but they are growing. This is called desertification and is caused by different reasons including human activities. The Sahara Desert is growing larger and larger each year. What should we do with it ?

    Our children and grandchildren may not have a chance to visit many of the most famous places around the world. War, weather, age, traffic and pollution damage (破坏) these famous places. If we do nothing, they may even no longer remain. But looking after these places often costs more than one country can afford.

    In the early 1970s, world governments decided that if they joined together, they would be able to preserve (保护) our history. If every country paid some money, they said, it would be possible to look after important historic places. For this reason, countries around the world united to form the World Heritage Organization in 1972. Today, the organization helps to protect and rebuild the most important places from our history.

    However, one of the biggest problems for historic places is vandalism. That is to say, people sometimes enter these places and damage the buildings. At some places, such as Stonehenge in England, governments have built high fences to protect it from vandals.

    There are many different ideas about how to solve the problem of vandalism. Some professors say that if guards keep walking around these places, vandals won't be able to get in. Some professors say that if they fix more television cameras, they won't need so many guards. Others say that the best way is education. If people learn to respect history, they won't damage it. They will also want to spend money looking after old places. For this reason, the World Heritage Organization helps to spread information about the value of historic places.

    Babies born after 2017 may never need to take a driving lesson because of the development of self ­driving cars. Some scientists say that self ­driving or driverless cars(无人驾驶汽车)may hit the roads within 15 years, and it is possible that driving may become unnecessary, or more relaxing and enjoyable.

    Companies like Google, Baidu, Apple and Alibaba are working on driverless cars. But, if the tests are successful, these electric self­ driving cars could be put into use very soon. This kind of cars may change the way we live in the future. All you have to do is to type in the address!

    According to Baidu, driverless technology has the following four advantages. Firstly, driverless cars are actually safer. With driverless cars, the number of deaths caused by accidents will decrease. Secondly, driverless cars are more efficient(效率高的) than manned cars. Thirdly, driverless cars follow the traffic rules. Therefore traffic control will be easier to achieve. At last, the cost of transportation will be reduced as the labor cost becomes less.

    There are many different technologies needed to make a successful self ­driving car. The most difficult technologies of all are environmental perception(感知), behavior prediction, planning control, HD mapping, and exact GPS.

    Technology is developing fast and it has become an important part of our life. Then what will the world be like in the future?

    3—D food will be both delicious and nutritious(有营养的). We can use 3—D printers to print some basic materials.    ①    And we can go further. Scientists belive that we just need to turn on a printer in the kitchen and then we can enjoy our favourite food whenever we like.

         ②      5G network will allow many more people to get information. Big companies like China Mobile and China Unicom will start to offer 5G. It is said that promises download speeds 10 to 20 times faster than 4G. For example, we can download a film within just 1 second. But with a 4G network, it takes a few minutes. There will be much bandwidth (带宽) and we can get unlimited (无限的) information.

    Underwater cities will provide more space. The earth is becoming more and more crowded. We may turn to underwater homes, which will be built as low as 15 of the sea can be used to provide power for the homes.

         ③      For us common people on the earth, the dream of travelling around space will come true. In the coming years, spacecraft will be as popular as buses, trains and planes. We can leave our home and enter space to take an adventure (冒险). And even we will get used to living there.

    A robot will be a part of life.  Robots can do many of the same things as we humans do like driving cars. But they will be used in other areas as well. They will be able to think. They can tell the difference between right and wrong. They can feel       ④        In a word, just as Jules Verne said, "Anything one man can imagine, other men can make real."

    Do you want to know what our life will be like in the future? Let's have a look. You may get a surprise.

    You will go to the kitchen when you are hungry. You will give orders to the kitchen robot. The robot will find a special food for you in a few minutes. Then it will bring it to you.

    In the kitchen you will find a special food machine. The food machine will tell you what your body needs. It will help you eat healthily. The food machine will be connected with (连接) the kitchen robot. The robot can get messages from the food machine.

    After having a meal, you can go to your home office. You will work at home and you don't need to go out to work anymore. You will have a special information screen. When you receive a message from a friend in America, your information screen will be turned on automatically(自动地). Your friend's face appears on the screen. Then you can talk to your friend easily.