The population of the Earth is growing faster. It is important that we look after the Earth. We need it!
The Earth gives us a lot of things. We also give the Earth a lot, but some of the things are not good.
In nature, when something dies, other animals and plants get food from it. Every animal or plant gives food for other animals or plants. However, animals can't get food from many of the things that we ‘give' the Earth. Animals and plants can't eat metal, plastic and glass. These things will stay in the ground for many, many years.

Some rubbish is very dangerous for plants and animals. In some places, many animals live together. One animal makes food for many more animals. If we put rubbish and chemicals in the water, the plankton(浮游生物) can die. If there isn't any plankton, many animals have nothing to eat.
So what can we do? Don't leave any rubbish in the countryside! Don't make so much rubbish!

    We often praise the world of science. It explains the world and makes our lives easier with technology. One of the most exciting fields in science is artificial intelligence (人工智能，AI). This is an area where scientists are working on creating machines that think like humans.

    However, one ofthe most famous scientists has a very dark warning for us about this type ofte chnology.

“The development of full artificial intelligence could lead to the end of the human race,” said Professor Stephen Hawking to the BBC.

    Hawking is a well-known British Physicist and writer of best selling science book A Brief History of Time. This warning came from a serious disease called ALS; he needs an AI computer to communicate. The computer learns how Hawking thinks and suggests the words he may want to use next.

    This is a basic type of AI, which is very useful, yet Hawking fears the possibility of creating technology that can match or go beyond human intelligence. And it's easy to imagine how terrible things may be. Many TV shows and films display big, killer machines that arefar cleverer than us. “Humans, who are limited by slow biological evolution(进化), couldn't compete, ” said Hawking.

But not every scientist is pessimistic(悲观的) about AI technology. “I believe we will remain in charge of（掌控) the technology. “ The potential(潜力) of itto solve many of the world problems will be realized.” In what direction do you think AI is going? Should we be hopeful or fearful?

    Dolphins are not fish, but warm-blooded animals. They live in groups, and speak to each other in their own language. In this they are like other animals, such as bees and birds. But dolphins are very different from almost all land animals. Their brain is nearly the same size as our own, and they live a long time—at least twenty or thirty year.

    Like some other animals, dolphins use sound to help them find their way around. They also make these sounds to talk to each other and to help them find food. We now know they do not use their ears to receive these sounds, but the lower part of the mouth, called the jaw.

    Strangely, dolphins seem to like man, and for thousands of years there have been stories about the dolphin and its friendship with people.

    There is a story about sailors in the 19^th century. In a dangerous part of the sea off the coast of New Zealand, they learnt to look for a dolphin called Jack. From 1871 to 1903 Jack met every boat in the area and showed it the way. Then in 1903 a passenger on a boat called The Penguin shot and wounded (伤害) Jack. He recovered and for nine years more continued to guide all ships through the area—except for The Penguin.

    Today, some people continue to kill dolphins, but many countries of the world now protect them and in these places it is against the law to kill them.

    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.