—Then let's____________ a taxi.

    Many people know that rubbish is a big problem on planet Earth. What many people don't know is that junk (垃圾) has become a problem in outer space too.

    According to BBC News, there are more than 22,000 pieces of space junk floating around the Earth. And these are just the things that we can see from the surface of the Earth by telescopes (望远镜). There are also millions of smaller pieces of junk that we can't see.

    Objects, like bits of old space rockets or satellites, move around the planet at very high speed, so fast that even a very small piece can break important satellites or become dangerous to astronauts. If the tiniest piece of junk crashed into a spaceship, it could damage the vehicle.

    To make things worse, when two objects in space crash, they break into many smaller pieces. For example, when an American satellite hit an old Russian rocket in 2009, it broke into more than 2,000 pieces, increasing the amount of space junk.

    To reduce additional space junk, countries have agreed that all new space tools can only stay in space for 25 years at most. Each tool must be built to fall safely into the Earth's atmosphere after that time. In the upper parts of the atmosphere, it will burn up.

    Many scientists are also suggesting different ways to clean up space junk. In England scientists are testing a metal net that can be fired into space junk. The net catches the junk and then pulls it into the Earth's atmosphere to burn up. The Germans are building robots that can collect pieces of space junk and bring them back to the Earth to be safely destroyed.

    "The problem is becoming more challenging because we're sending more objects into space to help people use their mobile phones and computers," says Marco Castronuovo, an Italian space researcher.

    "The time to act is now. The longer we leave the problem, the bigger it will become," he says.

    On April 2, we said goodbye to Tiangong-1, China's first prototype space station. According to the China Manned Space Agency (中国载人航天局), Tiangong-1 re-entered the Earth's atmosphere (大气层) and some of its debris (碎片) fell into the South Pacific Ocean.

    There are many spacecraft (宇宙飞船) that are still in orbit (轨道) above the Earth. After finishing their trips, they will all re-enter the Earth's atmosphere like Tiangong-1. There are two types of re-entries: controlled re-entry and uncontrolled re-entry.

    Some satellites and manned spacecraft come back to the Earth in a controlled re-entry. Experts calculate (计算) the path of the falling spacecraft and its speed. They can guide the spacecraft to fall in a chosen area.

    Some spacecraft may have problems while in space after a certain amount of time. These spacecraft come back in an uncontrolled re-entry. It is hard to tell when and where these spacecraft will fall until the last few hours. The US space station Skylab came back partially uncontrolled in 1979. Parts of the station fell in western Australia, but no one was hurt.

    During re-entry, most of the spacecraft will burn up while passing through the Earth's atmosphere. Only a small amount of the debris will reach the ground. The debris typically ends up falling into the ocean, China Daily reported.

    Andrew "Ender" Wiggin is a 6-year-old army general (将军), and a gaming genius. Sometime in the Earth's future, humans have a war with a bug-like alien species, the "buggers". They use computers to control wars. To prepare for the war, all talented children study in a special school to become generals. Wiggin is one of them.

    Students play games to practise their commanding (指挥的) skills. Wiggin is the best of them. At last, Wiggin comes to his final test. The fleet (舰队) he commands in the game is the real human army. Wiggin is actually "playing the final battle" between humans and buggers. Will he win? What will happen to humans after the battle? Let's find out in the book Ender's Game, by American writer Orson Scott Card.

We must finish our homework .

The man funny that pair of big glasses.

    I went to the seaside to spend my holiday last summer with my family. One day, I was swimming in the riversomeone shouted, "Look out. There is a shark not far away!" On (hear) the shout, I was very frightened because I was well aware of its (dangerous). "Just don't worry, Tom!" my father said to me, "but in order to be (safety), let's go back to our hotel."

    We stayed in the seaside for about two weeks. Though the weather was much (hot) than that in my home town, I got used to it and (feel) at home. Every morning, I got up earlier than my parents and went for breakfast ahead of time. Then I went to havechat with my new friend, John. John lived near the seaside he knew the seaside well. Soon we became very good friends. After I left, we (be) in touch with each other for a long time.

Now, I still often hear from him. We talked in our letters about things and persons we remembered in the seaside (happy).

    Artificial intelligence (人工智能) , or AI in short, is the science of giving computers and machines ability to think and work like humans.

    AI is rapidly catching up with the human ability to read faces. As a result, facial recognition (识别) is used a lot in the world. Chinese police use this technology to identify criminals (罪犯).It also checks the ID of ride-hailing (约车) drivers and lets people pay for things with a smile.

    Most drivers may wave or nod at passers—by to let them cross the street, but self—driving cars don't have this ability. Carmakers are testing a light signal system to help them "speak" to humans.For example, if a driverless car is yielding (让路) , it will flash two white lights side to side. A rapidly flashing light tells passers-by that the car is about to speed up.

    Service robots also show you how powerful AI is. Imagine this—you come back from school and your robot housekeeper is waiting for you at the door. After dinner, he teaches you to play the piano, just like a real music teacher. Such thoughts will soon happen in the real world.AI is so powerful that it can help human beings and even replace us in many jobs.