Ladies and gentlemen, I returned to this year in a time machine. In the year 2500, we are able to travel through time to any year in the history of the earth. This year is your last chance to change your lifestyle to save the earth.

    Beginning in the middle of the 20th century, a few people were worried about polluting the earth's water and air, but most people did not change their way of life.  Instead, they continued to pour(倒) dangerous chemicals and other waste into lakes and seas, to drive more and more cars and trucks, and to cut down trees.

By the year 2200, the earth's water was completely polluted. Scientists said that in the future there might be too many people on the earth. People could no longer drink water, and they had to use other types of liquids(液体).

So, by the year 2300, there were so many people that food became scarce. There was no water to grow food and all of the fish in the lakes and seas died because of pollution Terrier wars(战争) broke out between the rich and the poor. Scientists were working very hard to find another planet in space where humans could live on.

By the year 2400, the air was too polluted for humans to breathe. So we had to leave earth but only the rich were able to leave. Where did we go? Nowhere. And everywhere. You see scientists did not find another safe planet, so now we must travel around the universe in our space ships. We are still looking for a place to call our home.

    So, it is up to you to change history. There is still hope. You must change your lifestyle now, before it is too late.

    Birdwatching is becoming more and more popular in many parts of the world．

    Birdwatchers enjoy looking for and listening to different kinds of birds．To watch birds, all you need is a pair of binoculars, a field guide and love for birds．

    If you are just starting birdwatching, buy one of the cheaper pairs of binoculars．You can choose better ones when your needs and skills grow．A field guide helps you leam about the birds' appearances, calls and habits before birdwatching．

    When you are ready, it's best to go to the wild with someone who is more experienced．You can join a birdwatching group to learn about some beginning skills．A local bird club is ideal．

    Start birdwatching in the morning, when birds are searching for food．Most of the time, you will hear bird calls from all around you, but will not see any birds easily．Look for movement in trees, and bring your binoculars to your eyes．

    The most important work for a birdwatcher is to identify the birds he/she sees．A bird's shape, size, colour and habits can help a birdwatcher identify it．When you identify a bird, don't forget to take notes about it on your notebook．

    To find more and different birds, you may wish to plan trips to birds' different living areas： forests, lakes, rivers, wetlands, etc．

    When watching the birds, you should always keep in mind： respect wildlife and protect its living areas．

    You must think a computer is the best thing in the world, right? You must think it works at a super speed and can do everything? Well, it's not! In fact, the brain is much more powerful than any super computer! Think about when a glass is just about to fall off the table. Your brain controls everything that you need to do to save that glass from falling. First your eyes check out what's going on, then tell your brain, and your brain decides how quickly you need to react(反应), and then your muscles(肌肉) go into action. That is just from your brain. No computer could ever come close to that!

    The brain weighs just 3 pounds, but it controls everything you do from thinking, learning, feeling even to breathing and your heart beating. Even though the brain is just 2% of your body weight, it uses around 20% of all your energy in your body. That is a lot for such a small organ(器官). There are about 100 billion tiny, tiny little cells(细胞) in your brain. There are so many that it would take you over 3,000 years to count them all!

    Your brain stops growing when you're 18, but it actually keeps on developing and learning new things. So your parents are really super smart! You won't be able to fool them! Believe it or not, your brain NEVER stops working. Even during sleeping, the brain works for long-term memory establishment(建立). It is realized that the brain is the second organ in the body as the heart that never stops during human lives.

    So everyone should be proud of such a gift of nature.

    Have you noticed your life becoming a little easier? Now, when you go to a certain shopping mall, you can enjoy its free Wi-Fi there. When you want to take a taxi, you can book one with your phone. In fact, all these can be seen as the basic parts of a smart city.

    The idea of a smart city was brought up by US company IBM in 2010. Generally, a smart city is a city that uses digital technologies such as the Internet to improve city planning, save money and resources, and make our life convenient. How smart can a city be? Here are great examples that we can learn from.

    In 2009, Dubuque became the first smart city in the US. The city used smart water meters to take the place of traditional water me tens. They can detect (探测) water waste and leakage (泄漏) and send data to let the house owner know. The same system is used for other city resources like electricity and natural gas. In this way, people know how they use their resources and are glad to help reduce waste.

    Santander in Spain also gives us a look at the future. If people point a phone toward a nearby bus stop, the phone immediately shows all bus lines that serve the stop as well as their arrival times. The government organized a research team and provided an App (应用程序) that collects data on almost everything: light, temperature, and the movements of cars and people. Opening the App near a supermarket provides immediate information on special offers.