Lately, people have entered the forests where chimpanzees (黑猩猩) live. The chimpanzees have been getting sick because of people's diseases. In addition, people are hunting chimpanzees. Their number is becoming smaller and smaller.

Chimpanzees live in the plains and forests of Africa. They eat many kinds of food, from plant leaves and seeds to insects and even other small animals. Chimpanzees' favourite food is fruit.

    Chimpanzees are very clever and they can use tools well. They can catch bugs using sticks, and break nuts using rocks.

    The world's forests are much smaller than they were before. Roads were built in deep forests, so people start to enter forests where chimpanzees live. That may lead to many problems. One problem for chimpanzees is that they can easily catch people's diseases and die. Chimpanzees are much closer to people than monkeys.

As it's easier for people to enter forests, they hunt more often. Young chimpanzees are caught to be pets or for scientific researches. The young ones are taken away from the forests, and the adults are killed. Chimpanzees are likely to disappear in the future.

    The Earth is about 4, 600 million years old Man lives on the Earth for only 35, 000 years. But we change our Earth in many ways. Many things we do are good, but some are not good for the Earth.

    Water pollution

    A lot of people, birds and fish die each day because of water pollution. Factories pollute the water. As a result (因此), the water in many rivers and lakes is now very dirty.

    Air pollution

    In big cities, factories, cars and buses are the main causes of air pollution. Many people in cities now have health problems. For example, Mexico City used to be a beautiful sunny capital, but today there are many clouds in the sky. And many people get ill because of the polluted air.

    Soil (土壤) pollution

    In order to have a better harvest (收获), some of the farmers use chemicals too much in their fields. That's bad for the soil.

    Hope for the future

    These problems are very serious for our future, so all of us should do something to protect the environment. If we can stop pollution, our Earth will become more and more beautiful.

    A few years after World War Ⅱ finished, scientists spoke with great eagerness about the use of nuclear power as a source of energy. Within twenty years, they said, nuclear would take the place of coal, gas and oil as a source of power at home and in industry. This promise has never been carried out(兑现)and there are serious doubts that it ever will be. Nuclear power plants are used to produce energy in some wealthier countries, but the cost is high.

    Although safety measures have been taken, radiation leaks have taken place and workers have been killed or affected. The problem of getting rid of the nuclear waste has proved most difficult. There is a limit to the amount of waste materials which can be buried in the ground or poured on the sea-bed. These methods may also cause more problems. Waste materials polluted by radiation may remain dangerous for 200 years or more.

    It is no surprise that scientists have now turned to the sun and the sea as sources of power. The sun shines day after day almost wastefully, providing us with energy far be yond all our needs.

    A black hole is a place in outer space with very strong gravity. Gravity is a great force(力量) that shapes the universe. On Earth, gravity makes apples fall from trees. It keeps your feet planted on the ground. The gravity in a black hole is much stronger. It is so strong that nothing around it can get away from it, not even light.

    Black holes are invisible. We can't actually see them because they don't throw back light. But scientists can find them with space telescopes(望远镜)and special tools. The strong gravity makes nearby stars move in a certain way. By studying how the stars move, scientists can find out if they are flying around a black hole. Strange things happen around black holes. This makes black holes a popular subject of science fiction(科幻)stories, although they are very real.

    A black hole forms when a star dies. The star falls in on itself and turns into a very small point. Because of its small size and huge mass(质量), the gravity will be so strong that it will pull light in and become a black hole. Black holes can grow huge as they continue to pull other things in and "eat" them. Many scientists believe that there are super-massive black holes at the center of galaxies, including the Milky Way.

    The idea of the black hole was first suggested by two different scientists in the 18th century: John Michelle and Pierre-Simon Laplace. In 1967, a physicist named John Archibald Wheeler came up with the name “black hole". Studying black holes can tell us many things about our galaxy and help scientists answer questions about the universe.

    We can see walls everywhere in the world. But the Great Wall of China is the biggest of all. The Chinese call it "The Ten-Thousand-Li Great Wall". It is in fact more than 6000 kilometers long. It is 6～7 meters high and 4～5 meters wide. In most places, five horses or ten men can walk side by side along the top.

    When you visit the Great Wall, you can't help wondering how the Chinese people were able to build such a great wall thousands of years ago. Without any modern machines, it was really very difficult to build it. They had to do all the work by hand. It took millions of men hundreds of years to build it.

    The Great Wall has a history of over two thousand years. The men began to build the first parts of it around two thousand seven hundred years ago. Then QinShihuang had all the walls joined up. He thought that it could keep the enemy out of the country.

    Today the Great Wall has become a place of interest. Not only Chinese people but also people from all over the world come to visit it.