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    According to the World Health Organization (WHO), environmental pollution kills 1.7 million children under the age of five every year worldwide. The WHO warns that child deaths will increase greatly if pollution continues to worsen. Of all the environmental problems, air pollution is being called the most dangerous.

    Most of these deaths take place in developing countries. However, WHO environment and health chief Maria Neira tells that air pollution is a leveler between rich and poor. Everybody, she says, needs to breathe.

    “You can be a very rich child, your parents very rich, but living in a place, in a city, which is very polluted. Then there is very little you can do because we all need to breathe. Air pollution is everywhere.”

    Maria Neira says one of the most important ways to reduce air pollution is to produce cleaner fuels for cooking and heating.

    “Almost half of the world population is using dirty fuels for cooking, heating, and lighting at home. And, this is affecting very much mothers who are staying and cooking at home, but the children who are around mothers—they are exposed as well.”

    Cleaning up how the world cooks, heats and lights homes and other buildings is a big-picture goal.

    But what can every one of us do to limit our family to air pollution?

    The U.S. Environmental Protection Agency has the following suggestions:

    ● Avoid walking where there is a high volume of vehicle traffic.

    ● Equip homes with air filters and air conditioning units.

    ● Limit your time outside if you live in an area that issues warnings about air quality.

    ● Wear high-grade, rated face masks tightly to the face when air quality is poor.

    ● If you live or commute in a very polluted area, remove your clothes and wash immediately after entering your house.

    However, the WHO stresses that governments around the world need to take the lead on ensuring that children grow up in a clean environment.

    Alsten Chase has written a book about Yellowstone National Park. He is worried about the damage the fires can do to the park. He is also concerned(关心) about the park rules. These rules say that nature should decide what happens to the park. Alsten also writes that the elk herd(马鹿群) has grown too big. The elks walk on the riverbanks. They eat the new grass and roots of baby trees. The beavers(河狸) need the trees to build dams(坝).

    The dams raise the water levels. Higher water levels put more water into the soil. Wet soil helps plants grow faster. The plants offer homes and food to other animals.

    Chase thinks that the park rules would work only in a park with natural settings. He believes that Yellowstone has had an artificial(人为的) setting for a long time. The native people left. The wolves were taken away and other animals were removed. The areas of land were fenced off(隔开) and other animals added. He thinks the park rules that let herds grow too big and the fires are hurting the nature of the park.

    The park manager thinks the rules are good and that the park will be fine. Chase thinks the way the people run the park should be changed.

    Now, it seems that artificial intelligence(人工智能) is becoming more and more popular in our life, and it has greatly influenced the ways we live, work and play. Can you imagine that you can play table tennis with a robot one day?

    Recently, a scientist has invented a special robot that can be a table tennis coach. That means people can practice table tennis not only with humans but also with a robot.

    Named Forpheus, the smart table tennis robot is quite special. It can study the movements of human players and the speeds of the ball. In this way, it can exactly judge(判断) the players' skill levels(水平).Then it uses the information to change the ways to play. If the players are just beginners, Forpheus will play in a slow and easy way, but if the players are better ones, the robot will play in a faster and more difficult way. What's more，while playing, it encourages players 10 try their best with words like "Good job!" "Come on!" and so on. At the same time, it gives some good advice to improve their sill so it is a good partner and clever coach.

    Science and technology is developing quickly these days and it's hard to imagine what will happen in the future." In the next 20 years, it will be possible that one robot teaches another to play table tennis or even invents another one!" Takuoya, the inventor of the robot, said.

    The movie The Martian (《火星救援》) is very popular among space lovers. It shows an astronaut trying to live on Mars.

    Although the idea of living on Mars is great, the reality does not look so good. Mars does not have a friendly atmosphere (大气层) for humans. There is very little oxygen there. And because it is too far away from the sun, it is also very cold there. Sometimes the temperature on Mars can be -133℃. This is much too cold for humans.

    However, scientists say it might be possible to live there even without a good atmosphere. Daytime on Mars is almost the same as Earth's. It means there's enough sunlight to grow plants inside safe buildings. However, they would have to grow in soil from Earth. Mars does not have a strong enough atmosphere to stop the radiation (福射) coming from space, which makes it dangerous to grow things in the soil.

    The radiation also causes problems for our health. One way to live there is to build homes underground or in the rocks on the planet. This can help humans keep away from the radiation and keep warm.

    When could we live on Mars? Scientists are hoping to make it possible to live on Mars. Let's wait and see.