— ________________ them ________________ over one hundred.

    Do you know who invented paper? A Chinese man1Cai Lun invented paper almost 2,000 years ago. He made paper2wood.

    Now we still use wood3paper. We use a lot of paper every day. If we keep on4so much paper, there will not be any trees left on the earth. If5no trees, there will be no paper. Every day, people6about 2,800 tons of paper. We use 17 trees to make one ton of paper. This means we are cutting nearly 48,000 trees every day.

    Since it7more than 10 years for a tree to grow, we must start using8paper now. So how can we save paper? We can use both sides of9of paper, especially when we are making notes. We can choose drinks in bottles instead of those in paper packets. We can also use cotton handkerchiefs (手帕). When we go shopping, we can use fewer paper bags. If the shop assistant gives us a paper bag, we can save it and reuse it later.

    Everyone can help to save paper. If we all think carefully, we can help10trees. But we should do it now, before it is too late.

    Can trees talk? Yes—but not in words. Scientists have reasons to believe that trees do communicate with each other. Not long ago, researchers learned some surprising things. First a willow tree (柳树) attacked in the woods by caterpillars (毛毛虫) changed the chemistry of its leaves and made them tasteless so that the caterpillars got tired of the leaves and stopped eating them. And the tree sent out a special vapor—a signal causing its neighbors to change the chemistry of their own leaves and make themselves taste also terrible too.

    Talking, of course, doesn't need to be always in words. We can talk to each other by smiling, raising our shoulders and moving our hands. We know that birds use a whole vocabulary of songs, sounds and movements. Bees dance their signals, flying in certain patterns that tell other bees where to find nectar (花蜜) for honey. So why shouldn't trees have ways of sending messages?

    Trees are important and they can help us in many ways. However, some of them are in danger and need to be taken care of as much as possible. There are some ways to save trees.

    Use paper wisely. We can save trees by using paper in a right way. What can we do? Use both sides of paper when doing homework. Borrow books to read when you needn't buy them. Never throw old books away, but be kind to donate them to others who need them. Use cloth towels instead of paper towels.

    Plant trees. To save trees, it's a great idea to plant them. Spring is the best season to plant trees. If everyone around us does it, millions of trees will appear and make our world become green and beautiful.

    Tell people to understand the importance of trees and help save trees. Try to write letters to government officials (官员) and persuade (劝) them to use as little paper as they can.

    Trees are an important part of the Earth. They provide wood for buildings and things for making paper. They provide homes for all kinds of insects, birds and other animals. For example, many birds live in trees. Many kinds of fruits come from trees, such as apples, oranges, pears and peaches.

    Trees also help keep our air clean and our ecosystems healthy. We breathe in oxygen and breathe out harmful gases. However, trees breathe in harmful gases and breathe out oxygen. And trees can help other plants grow because they can hold the soil. Trees keep the soil from being blown away, so plants can fight against strong winds.

    Trees do much for us, our environment, other plants and animals, but we don't just love trees for that. Trees can also be very beautiful—tall enough to touch the sky and so big around that we can't even hug them. So we should stop cutting down trees and enjoy the beauty of them.

The bed                    wood.

I             the classroom and didn't see anybody.

             , she told a lie.

I like doing sports. It                    us.

             tourists come to Guangzhou every year.

    Every year a large part of rainforests disappears on the Earth. There were lots of plants and animals       years ago. But now many of them die. Other animals have to leave and find a new forest to make their home. Why do the rainforests disappear       ?

    The main reason is that people destroy rainforests. People cut down many trees in the rainforests every year. They use the trees       and paper. Farmers need to grow food and keep animals, so they turn rainforests into farms.

    The drought (旱灾) is bad for rainforests too. In 2010, a big drought happened in the Amazon Rainforest. Rivers dried up and millions of plants and animals died. The drought also made the air       the forest fire happened easily. Many animals lost their homes because of the fire.

    It's time to protect the rainforests. All of us should       the forests to make the world more beautiful.

    Some countries are building a great wall of trees across Africa. It is called the Great Green Wall. The aim is to bring life to the dry lands and help to fight the bad environment.

    The wall is about 8,000 kilometers long and about 15 kilometers wide. It covers from Senegal in the west to Djibouti in the east, on the south of the Sahara Desert (撒哈拉沙漠). So far, Senegal has made the best progress by planting about 11,000,000 trees.

    Many years ago, there were few trees in that area and the winds used to be very strong. It was harmful to the fields. Also, there was little rain, so few plants could grow and many people went hungry. Since the tree planting project started, the trees have provided food for the local people and increased the wetness (湿度) of the air. Little by little, there appeared green fields for people to grow plants.

    The project which began in 2007 is supposed to cost a total of 8,000,000,000dollars. Many countries are trying their best to help to continue the planting. So we will be able to see the whole green wall across Africa in the near future!

提示：1）树可以为我们提供很多有用的东西，如水果、药品、木材等；2）树可以为人类提供氧气，净化空气，美化环境；3）树可以为动物提供家园和足够的食物，保持大自然的平衡（the balance of nature）；4）树能够防止水土流失和土地变成沙漠（desert）。

The uses of trees

    For humans, trees have a lot of uses.