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.

    There are many kinds of 1. transportation now. Which one do you like best, by train, by bus or by plane? Now let's look at these three kinds of transportation. 2.The fastest way to travel is by plane. If you want to save time, 3.乘火车是最好的选择. A plane ticket can also be easier to book, and there are 4.(hundred) of planes leaving half an hour to everywhere. But it is much 5.(expensive) than traveling by train or by car. Many people prefer to traveling together by train. Because the train is cheaper than the plane and you can see the beautiful scenery out of the windows. But sometimes people are very noisy on the train. And it's very small and crowded inside the train. Taking a car is great. You can feel freer in your own car and you can move quickly from place to place at any time you like. 6.But sometimes you may be late because of the heavy traffic  .You have to pay for a car park and petrol . Cars are less comfortable than trains. You can't sleep or relax when you drive. Cars pollute the air more than trains, too.

    Lockheed Martin, American space system company (空间系统公司) has found a really cool way to inspire the young minds of today to the research fields in Science, Technology, Engineering and Math (STEM).

    It may look like a normal yellow bus, but all the magic happens once you get inside. Meet the “Mars (火星) Experience Bus,” part of Lockheed Martin's new “Generation Beyond” national education program to get the kids joining in studying what goes on outside of our home planet. The bus offers a virtual reality (VR, 虚拟现实) experience making the teenagers feel like they are driving on Mars.

    The VR experience was developed by taking advantage of software (软件) created for today's best video games, so you can imagine the picture shown is top level. The kids do seem really excited to see the bus take a virtual trip on the red planet and search unknown places. It's certainly a great way of learning about the universe by virtual reality working on a common bus.

    The Lockheed Martin's bus will start a tour in the United States to allow kids from different parts of the country to take a ride in it. The Generation Beyond project also includes an iPhone app for iOS providing real-time information about weather reports for Mars, and there's also a free deep space course for middle school teachers and students.

    People can use the phone to talk with others almost anywhere on the earth. But when you use the phone, you don't see the person you are talking with.

    Today some people are using a kind of telephone called the picture phone or vision phone. With it, two people who are talking can see each other.

    Picture phones can be useful when you have something to show the person you're calling. They may have other uses in the future. One day you may be able to ring up a library and ask to see a book. Then you'll be able to read the book right over your picture phone. Or you may be able to go shopping through your picture phone. If you see something in the newspaper that you think you want to buy, you'll go to the phone and call the shop. People at the shop will show you the thing you're interested in right over the phone .You'll be able to shop all over the town and never even leave your room.

    Height is just one of the features your genes(基因) decide. In fact, because you have two parents, your genes provide you a height that usually lands somewhere between the height of each parent. If both your parents are tall, then most probably you will be tall, too. But if you have questions about how tall you're going to be, ask your doctor if he or she can help you find them out.

    But genes don't decide everything. For example, eating an unhealthy diet can keep you from growing to your full potential(潜力). Getting plenty of sleep and enough exercise will help you grow to the expected height.

    It's natural that you're wondering how fast you should grow. There's no perfect or right answer. Generally speaking, kids grow about 6 cm a year between age 3 and the time when they start puberty.

    Your doctor will know how your growth has been going over the years. 2 cm here and 3 cm there make a little difference to the height you're at now. How have you been growing up to this height? What other changes may your body be going through?

    Don't be amazed if you seem to have grown a lot in a very short time. Everyone has a growth spurt(高峰) during puberty. The age for starting puberty is about 10 for girls and about 11 for boys. But it can be earlier or later — between 7 and 13 for girls and 9 and 15 for boys.

    You'll usually begin to notice that you're growing faster about a year after your body starts to show the first changes of puberty.

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    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.