Today some people call Amsterdam the "City of Bicycles" because it is a city which is flat and convenient（方便）for bicycles.

    In the 1960s, a group of cycling fans1an idea . They believed that it would be better for everybody if only bicycles were allowed in the city centre. They were2that this would help to save energy, reduce pollution and provide free public transport. The group painted hundreds of bicycles3and placed them in public places around Amsterdam for people to use.4was allowed to take them and use them for short journeys, whether he was a local or a foreigner, Wherever someone finished a journey, they would5the bike there for someone else to use. The problem was that it didn't work-thieves took all the bicycles6 weeks!

    7,more than thirty years later, the "white bike" is back in town-this time with a computer chip(芯片)to8 its every move! To take a bicycle, you have to put a special card inside. The new "White bike" is not white any more but is an unusual9with bright colours. The bikes are parked at special parking places and people who want to use them have to take them to another place that has enough room.

    There is already less traffic in central Amsterdam, 10 both locals and tourists have been using the white bikes. Thanks to the good ideas of lots of people, like the cycling fans in the 1960s, many people around the world have been enjoying city centre streets without cars for many years.

    In the past， many students practiced English with their pen friends — they sent letters to people all around the world. However， we now send emails to others and chat with people who live quite far away on the Internet.

    Here's some advice on how to succeed in your online language exchanges：

    How to start a conversation when speaking English online When you speak to somebody online， start by asking “Yes or No” questions. Use questions such as “Do you like …?” or “Can you …?” or “Have you ever …?”

    Remember your goal. You are trying to learn about the other person. Think about things you enjoy and try to find some common ground between you. And share your own experiences to show that you have similar interests. If you only ask questions， you will sound like a policeman or a policewoman!

    How to keep a conversation going “Listen” carefully. In that way， you can get to know somebody well. When you know him or her well， you will have more to talk about.

    Then ask follow-up questions. After you “listen”， use what you “hear” to learn more about that person. Use “open ended” questions， such as “What do you think of …?” or “What was the most interesting experience ...?”

    Remember some basic rules for online language exchanges.

    Be patient. Do not try to find a good friend right away.

    Be careful. Don't give any personal information on the Internet， especially your address， telephone number， and even your real name.

    Sharks (鲨鱼) are the most frightening animals in the sea. Sometimes we can see sharks swimming in the sea around Hong Kong. People put nets around some beaches to protect swimmers. When there is a "shark's flag", people must stay on the beach. It will be too late if a shark can swim sixty kilometers an hour to you.

    There are 30 kinds of sharks and 25 kinds of them are dangerous. The whale sharks are very big. They can grow to 18 meters long, but they are not dangerous to people. The jaws (大白鲨) and the tiger sharks are the most dangerous kinds of sharks.

    Do you know all sharks must keep swimming, or they will go down? All sharks can feel everything that happens around them. We must keep calm and don't make any noise when a shark is swimming near you.

    If a shark loses a tooth, a new one will grow out very quickly. So sharks always have many sharp teeth.

    The population of the world is still going up and scientists are worried that there will not enough food for us in the middle of the century. One plant from Madagascar, the Kalanchoe fedtschenkoi, may help. It takes in carbon dioxide (二氧化碳) at night and it needs 10 times less water than food plants like rice. This means it can grow in the desert(沙漠).

    It is dangerous to eat this plant, but scientists can study two things about it: how it takes in carbon dioxide at night when other plants only do this during the day, and why it is so good at living in the desert. There will be less good land for growing food in the future because deserts are increase in size. There, growing plants will be more and more important.

    There is a possible way to take this research. To grow a desert plant to eat will be difficult, but it may be possible to use the genes(基因) from this plant and put them into food plants like beans or potatoes. And the food plants with the genes can grow in the desert. We hope the plant could be an answer to our future food.

    We often find that weekends and holidays feel so short while classes and work feel so long. Actually, though, we know that this is not true. But we still wonder where that strange feeling comes from.

    In fact, this is one of the ways that we're tricked by time, according to the website. All that S interesting. The website lists several wrong impressions (印象) we often have about time. Let's have a look.

    First of all, emotions affect (影响) our time-keeping abilities. Negative emotions (消极情绪). especially anxiety and boredom, make time seem longer because they make us concentrate (集中) more on the passage of time. However, when we are enjoying ourselves, we pay more attention to what we are doing and are likely to lose track of (失去对……的意识) time.

    Here is another example. In 2007, a group of scientists carried out a test. In the test, people fell 50 meters into a safety net and were then asked about their experience. Although the experience took shorter than 3 seconds, the people thought it was much longer than it actually was.

    This is because of the way our bodies reply to danger, according to the scientists. Our bodies produce a chemical called adrenaline (肾上腺素) when we are faced with danger. It allows us to concentrate better so that we can stay alive. As a result, we are able to remember far more details (细节) over a short period of time, which makes it seem like time is going more slowly.

    Another situation when we make mistakes about time is when we take afternoon naps (午觉). Have you ever had trouble telling what time it is after a long nap? That's because the best amount of time for a nap is 20 minutes. After 20 minutes, you enter a new stage of sleep called slow-wave sleep. If you wake up mid-way in this stage, it will take a while before you can correctly perceive (感知) time again.

    Yes, time can be mysterious (神秘的) and there is no way to control it. So, perhaps the best thing to do is to make good use of every minute.