There are many kinds of animals that live in the forest, such as mice, rabbits, squirrels, bears.

    Animals in the forest depend on（依靠）one another for food. Many small forest animals, such as mice, eat green plants for food, and then larger animals eat them. This is called food chain. A food chain begins with the sun. The green plants in the forest use the sun's energy to make food for themselves. It's called photosynthesis(光合作用). Mice eat flowers and seeds that forest plants produce(生产).The mice get their energy from the plants, and the mice become food for a larger animal, such as the hunting hawk. So the energy from the sun passes from the plants to the mice to the hawk. A break（中断）in any part of this food chain means some animals may not have enough food to eat.

    The world itself is becoming much smaller by using modern traffic and modern communication equipment(通讯设备). Life today is much easier than it was hundreds of years ago, but it has brought new problems. One of the biggest is pollution. To pollute means to make things dirty. Pollution comes in many ways. We see it, smell it, drink it and even hear it. Man has been polluting the earth. The more people, the more pollution. Many years ago, the problem was not so serious because there were not so many people. When the land was used up or the river was dirty in one place, people moved to another place. They are slowly polluting the whole world.

    Air pollution is still the most serious. It's bad for all living things in the world but it is not the only one kind of pollution. Water pollution kills our fish and pollutes our drinking water. Noise pollution makes us angry more easily.

Many countries are making rules to fight against pollution. They stop people from burning coal in houses and factories in the city, and from putting dirty smoke into the air.

Pollution by SO₂ is now the most dangerous kind of air pollution. It is caused by heavy traffic. It is sure that if there are fewer people driving, there will be less air pollution.

    The earth is our home. We must take care of it. That means keeping the land, water and air clean. And we must take care of the rise in population at the same time.

    Lasers（激光） have many uses including improving someone's eyesight, playing DVDs, cutting the diamonds（钻石） and the list goes on and on. Now, there could be a new use for this powerful tool-changing the weather!

    The Swiss scientist Jean Pierre Wolf is working on using laser beams（激光束） to change the weather for the better. He wants to use it to help stop climate（气候） change. Sounds crazy, right? Well, there is already something kind of like it.

    Cloud seeding（云催化） is a way people stop rain from falling. It uses rockets to release chemicals into the atmosphere（大气层）, but it's not known what this might do to the environment. So Professor Wolf wants to find a better way to do this, and a laser is a good choice since the only thing it uses is light, not chemicals. But how would it work? According to CNN, it would make new clouds. The laser would make condensation（冷凝） happen, in other words producing drops of water. And then the water would turn into really small pieces of ice. Then clouds start to be made just naturally.

    Professor Wolf's hope is to help control the weather in places like California that can face both heavy floods and droughts（干旱）.They are also trying to use lasers to control lightning. Using lasers to change the weather has been tested in a lab, and they have been quite successful in some fields. They are still trying to find out how to use it in the real world, but it could be a new way to stop climate change. "Every time you think you have done everything you can with lasers, something new comes up," said Professor Wolf. "It's quite amazing."

    Here I want to tell you some informationabout water.

    Water covers most of our planet. People canfind it in oceans, lakes and rivers, and under the ground. Water moves in theenvironment by evaporation, condensation, and precipitation. The warm Sun helpswater change into vapour and rise up into the sky. It is evaporation. Thevapour in the air forms clouds in the sky. It is condensation. When the cloudsget heavy enough, the water falls back to the ground as rain or snow. This isprecipitation.

    Ocean water has too much salt in it. Muchof the water travels far over the land. When it travels over the land, thewater picks up salt from the rocks and soil. About 97.5% of the Earth's wateris salty water. It is expensive to take salt out of the water.

    All people need clean water. They need itfor drinking, for cooking, and for bathing. Some people in a village in SouthAmerica did not have clean water. Their water was full of oil and dirty things.People there got sick when they drank the water. Other people heard about theproblem. They sent empty water tanks (储水池) tothe village. Rainwater fell into the tanks. Now the people in that village havethe clean water.

One of the things to be learnt in a foreign language is guessing. You guess what kind of thing to come when listening to someone talking. People do this all the time in their own language, so it is necessary(必要的) to do this in a foreign language, too. Here are some examples.

1. " What's thematter?""I went to a party last night, so I…"

2. "I feel so tired these days. "" I think you'd better..."

3. " Of course, she never stops talking. She is one of the most..."

You can see from the above three examples that the context(上下文) helps a lot in understanding what is being talked about. So" guessing " is very important in understanding English, especially(尤其) spoken English.