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 ?

    A city without cars would be very strange, right? But Venice is such a city.

    Venice is in the northeast of Italy. It wasn't built on land, like Beijing or Shanghai, but on more than 110 islands. Seawater is everywhere around the city.

    Even so, travel isn't difficult. The waterways have always been the best way to get around. There are 117 waterways and more than 400 bridges that can guide you where you want to go.  People in Venice move from place to place by boat.

    Water makes the city special, but it is also a big problem. Sometimes tourists will have such strange experiences. One moment they walk across the Rialto Bridge, and there's nothing special. But when they come back to the bridge an hour later, it's underwater and everyone is wearing rain shoes.

    Once, people used too much underground water. This made the city get lower little by little. Now the city has gone down by 23 centimeters. Another problem is the rising seawater. The temperature has risen over the years. This has made the ice of the Arctic Ocean (北冰洋) melt( 融化). Every year, high waters hit the city in autumn and winter. When a lot of water comes, more than half of the city is underwater.

    Scientists are trying different ways to stop the city from getting even lower. The Italian government has asked some of Italy's biggest companies to build the MOST project, which was planned to be build under the seawater to stop the rising water. Anyway, this project is helping solve the problem.

    How green are you? Do you know how to be green?

    We all need a healthy environment, but we produce waste every day and it does harm to our environment.Though we are young, we can still do something to help. In fact, even the simplest everyday activities can make a real difference to the environment.Here are some ideas for you.

Reduce

    Reduce means “use less”.Don't waste things.This saves money and reduces pollution and waste going into the environment.Before we buy something new, think whether it is really neces sary or maybe the old one will be just as good! When we do buy things, choose local products if possible, and try not to buy too many things from abroad.

Reuse

    Reuse means "use again".Use things for as long as possible.When we buy things, make sure that they can last a long time.We should look after them so that they will last, and we should repair them if we can instead of throwing them away and buying new ones.Don't use a paper cup or a paper bag.It's better to use a china cup and a lunch box because you can use them again.

Recycle

    Recycle means “change things into something else”.Though it takes energy to change something into something else, it's better than throwing things away or burning them.Find out what can be recycled in your neighborhood and take part in the recycling program.We should also buy products made from recycled materials,such as recycled paper, to help save trees.

    So please remember three words: reduce, reuse and recycle.

    Today people can use the phone to talk with others almost anywhere on the earth. But when you use the phone, you don't see the person you are talking with. That may change in the near future.

    Today some people are using a kind of telephone called the picture phone or vision phone. With it, two people who are talking can see each other.

    Picture phones can be useful when you have something to show the person you're calling.

    They may have other uses in the future. One day you may be able to ring up a library and ask to see a book. Then you'll be able to read the book right over your picture phone. Or you may be able to go shopping through your picture phone. If you see something in the newspaper that you think you want to buy, you'll go to your phone and call the shop. People at the shop will show you the thing you're interested in right over the phone. You'll be able to shop all over the town and never leave your room!

    1970 was World Conservation(保护) Year. The United Nations wanted everyone to know that the world was in danger. They hoped something could be" done.

    Here is one example of the problem. At one time there were 1,300 kinds of plants, trees and flowers in Holland(荷兰), but now only 866 are left. The others have been destroyed (毁灭) by modern people and their science. We are polluting earth, air, water and everything around us. We can't live without these things. If things go on like this, we shall destroy ourselves.

    What will happen in the future? Perhaps it's more important to ask "What must we do?". More and more young people have known this. Many of them are helping to save our earth. For example, they plant trees. In a small town in the United States a large group of girls cleaned the banks of 11 kilometres of their river. Young people may hear about conservation through a song called "No one's going to change our world". It was made by Cliff Gichard and other singers. The money from it will help to conserve tigers, elephants and pandas on the earth.

    The best time to collect green leaves is early in summer but not so early. The months of June and July provide the best leaf samples (样本) but you can find great leaf samples throughout the summer. To make a full colour collection, you have to collect leaves in autumn. I have seen many beautiful fall colour collections.

    When you select leaves for your collections, try to select leaves of about the same size and shape on the tree. Make sure you should collect the complete leaves.

    Remember, simple leaves have only one blade (叶片) or leaflet. Compound leaves have several or many leaflets. You must know these two kinds of leaves. Good leaf collections contain the entire leaf. That is a small part of the twig (嫩枝) with a lateral or terminal bud (芽).

    When you collect leaves in the field, you can place them between the pages of a magazine to protect them. And then, press them as soon as possible before you remove them from this magazine. You should dry the collected leaves carefully before placing them in a leaf press. Finally, place them in a leaf press. You should write down each leaf's name and these names should follow the leaves until the exhibition comes.