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 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 chemical(化学物品) 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. People could no longer drink water, and they had to use other types of liquids(液体). Scientists said that in the future there might be too many people on the earth. But not enough was done.

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 lakes and seas died because of pollution. Terrible wars broke out between the rich and the poor. Scientists were working very hard to find another planet in space where humans could live.

By the year 2400, the air was too polluted for humans to breathe. So we had to leave the 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.

    Once people thought that dinosaurs were brown or gray in colour, but the answer is to be found out. After examining the remains of a dinosaur, scientists say the colour of the feathers is bright. American and Chinese scientists rebuilt the feathers of a flightless(不能飞的)dinosaur

that lived about 150 million years ago, and researchers studied melanosomes(黑素体)in the feathers. The researchers compared them to the melanosomes that control the colour of feathers on modern birds. They were then able to make out the colours of dinosaurs' feathers. Richard Prum, a biologist(生物学家)at Yale University, said the dinosaur would be a beautiful creature if it were still alive. The discovery is useful to scientists in another way. It helps them better understand not only how dinosaurs looked but also how they lived in their daily life. Some researchers plan to use this way to study the colours of other feathered dinosaurs.

    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.

    We always think that it's OK for us to leave our plants home during our vacation as plants won't scream like pets, right?

    A recent study done by a group of scientists at the Tel Aviv University has discovered that some plants will scream when they are under stress.

    The research was carried out on tomato plants and tobacco plants by cutting their stems (茎) and depriving (剥夺) them of water. A microphone was placed 10cm away from them. When their stems were cut, the plants started "screaming" between 20 and 100 kilohertz, and the scientists guess that this scream is probably meant to warn other plants nearby.

    When the tomato plants' stems were cut, 25 ultrasonic (超声的) pain sounds were recorded in an hour, and at the same time, 15 ultrasonic pain sounds were recorded from the tobacco plants. When they were deprived of water, the tomato plants recorded even more pain sounds with 35 pain sounds in an hour while the tobacco plants recorded about 11 pain sounds.

    The plants also acted differently to different kinds of stresses. For example, the tobacco plants gave out a stronger "scream" when they were deprived of water than when their stems were cut. But plants that were in no immediate (立刻的) danger gave out less than one ultrasonic sound per hour.

    The group of scientists said that plants are not as quiet as we had always thought, but in fact their voices are so high-pitched that we just can't hear them.

    Last year, another study has found out that plants feel pain when they are touched or hurt and they will give off a terrible smell.