Hundreds of years ago, life was harder than it is today. People didn't have modern machines. There was no modern medicine, either.

    Life today has brought new problems. One of the biggest is pollution. Water pollution has made our rivers and lakes dirty. It kills our fish and pollutes our drinking water. Noise pollution makes us talk louder and become angry more easily. Air pollution is the most serious kind of pollution to all living things in the world.

    Cars, planes and factories all pollute our air every day. Sometimes the polluted air is so thick that it is like a quilt (被状物) over a city. This kind of quilt is called smog.

    Many countries are making rules to fight pollution. Factories must now clean their water before it is thrown away, and they mustn't let dirty smoke go into the air.

    We need to do many other things. We can put waste things in the dustbin and do not throw them on the ground. We can go to work by bus with our friends in the same car. If there are fewer people driving, there will be less pollution.

    Rules are not enough. Every person must help to fight pollution.

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    Saving the Earth shouldn't be so difficult，if we can do the following．

    First，we should take our time ． There is no need to hurry．We can walk or ride a bike to work．

    Second，we should smell the Each．Open the windows．Turn off the air-conditioner, and at the same time，save the energy．

    Third，we should enjoy cooking at home and having meals on our dinner table．So we can use our own bowls and chopsticks，not the plastic ones．

    Fourth，we should spend our weekends and holidays in the park playing games and just riding a bike around.

    Fifth，we should learn how to use old things well in the house，in the garden，or in the kitchen．

    Lastly, no one really has a mountain and a sea．Don't throw rubbish here and there．

    In recent years, there have been many breakthroughs in the AI (人工智能) field. Here, let us see four of the most interesting developments in AI in 2017.

    Is there intelligent（有智力的）life on other planets? For years, scientists said "no." or "we don't know." But today this is changing. Seth Shostak and Alexandra Barnett are astronomers（天文学家）. They believe intelligent life exists（存在）somewhere in the universe. They also think we will soon contact them.

    Why do Shostak and Barnett think intelligent life exists on other planets? The first reason is time. Scientists believe the universe is about 12 billion years old. "This is long enough for other planets to have intelligent life, "say Shostak and Barnett. The second reason is size the universe is huge. "Tools like the Hubble Telescope（哈勃望远镜）have shown that there are at least 100 billion galaxies, "says Shostak. "And our galaxy, the Milky Way, has at least 100 billion stars. Some planets going around these stars might be similar to the earth. "

    In the past, it was hard to look for signs of intelligent life in the universe. But now, powerful telescopes（高倍望远镜）allow scientists to discover smaller planets-the size of Mars or the earth-in other solar systems, these planets might have intelligent life.

    Have beings from space already visited the earth? "Probably not, "says Shostak. "It's a long way away. However, intelligent beings may contact us in other way, such as radio signals（信号）. In fact, they may be trying to communicate with us now, but we don't have the right tools to receive their messages. However, this is changing. By 2025, we could make contact with other life forms in our universe and we might help each other. "

    When you look up into the night sky, you can see the moon. But do you know that you're only seeing one side of the moon? The other side, also known as the far side of the moon, has long been a secret to us. But now, we have a chance to see what's on the far side.

    On January 3rd, China's Chang'e 4 probe(探测器) landed on the far side of the moon. It is the first probe in history to land there.

    Chang'e 4 probe has already done a lot of things on the moon. One of its jobs is to grow plants. Chang'e 4 probe took six living things to the moon. Such as cotton, potatoes and fruit flies(果蝇). The cotton has already started growing. This is the first time humans have grown plants on the moon.

    Chang'e 4 probe also took a lot of pictures of the moon's far side. With these pictures, scientists will learn more about the moon.