Canada 4:00 a.m. to 8:00 a.m.

    Canada is a big country with six time zones. In the west, it is four a.m., and everyone is asleep, but in Halifax on the east coast it is eight o'clock and people are having breakfast. It is a cold Friday morning in November, and the temperature is ten degrees below zero Centigrade(度).
Argentina 9:00 a.m.
    In Buenos Aires, the capital of Argentina, it is nine a.m. on a warm summer morning, and people are starting work or school. November is a summer month in Argentina because it is in the southern hemisphere(半球).
Scotland 12:00 noon
    Scotland is part of the United Kingdom. The capital of Scotland is Edinburgh, and the capital of the UK is London. It is twelve noon, or midday, in Edinburgh. Children are having lessons, but they are looking forward to the weekend because there is no school on Saturday and Sunday.
Egypt 2:00 p.m.
    Friday is already the weekend in Egypt. Friday is a special day for Muslims, so schools, offices and shops are closed in all Arab countries. So now, at two p.m., most people in Egypt are having lunch with their families.
Japan 9:00 p.m.
    Japan is seven hours ahead of Egypt, so it is already Friday evening there. The weekend is beginning. Most people are out with friends or watching television or playing computer games.
New Zealand 12:00 midnight
    It is late on Friday night, so most people are asleep. Now Saturday morning is arriving. It is morning in Canada too, but that is Friday morning!

    What was discovered by accident? The answer is penicillin (青霉素). It kills germs. By killing germs, it saves lives. Suppose you are sick. You go to a doctor. She examines you. She says you have a "staph" infection (葡萄球菌感染). She gives you some medicine. You take it. The medicine knocks out the staph. Soon you are well. Before penicillin, this would not happen. Staph was almost sure death.

    Everyone wanted a medicine. Laboratories worked day and night. They grew the staph in small dishes. Then they tried to kill it. Nothing worked.

    The laboratory dishes had covers on them. They kept things from falling into dishes. Molds (霉菌) were a big worry. They are always in the air. You can't see them. They're too small. There are thousands of different molds. Molds can make an experiment fail. That's why dishes are covered.

    Dr. Alexander Fleming was working to kill the staph germ. He worked for years. One day he took a cover off a dish. He looked inside. There was a thick growth of staph germ. There was also some mold. Then he saw something strange. Where the mold was, there was no growth of staph. This is what Fleming probably thought. "By accident, I found a mold to kill the dreaded staph."

    This is how penicillin was found. But here's the real miracle. There are thousands of kinds of molds. But only one kind can kill staph. The mold must have fallen into the dish a few days before. The cover was probably off only a few seconds. In those few seconds the right mold fell into the right dish. Another man might have thrown the dish away. But Fleming was very careful and smart. He understood what the mold did. How lucky the humans were!

     The world itself is becoming much smaller by using modern traffic and morden communication means (工具). Life today is much easier than it was hundreds of years ago, but it has brought new problems. One of the biggest problems is pollution. To pollute means to make things dirty. Pollution comes in many ways. We see it, smell it, drink it and even heart it.

    Man has been polluting the earth. The more people have, the more pollution becomes. Many years ago, the problem was nor so serious because there were not so many people. When the land was used up or the river was dirty in one place, man moved to another place. But this is no longer true.

    Man is now slowly polluting the whole world.

    Air pollution is still the most serious. It's bad for all living things in the world, but it is not the only one kind of pollution, Water pollution kills our fish and pollutes our drinking water. Noise pollution makes us angry more easily.

    Many countries are making rules to fight pollution. They stop people from burning coal in houses and factories in the city, and from putting dirty smoke into the air. Pollution by sulfur dioxide (So₂) is now the most dangerous kind of air pollution. It is caused by heavy traffic. We are sure that if there are fewer people driving, there will be less air pollution.

    The earth is our home. We must take care of it. That means keeping the land, water and air clean. And we must pay attention to the rise in pollution at the same time.

    Have you ever had trouble sleeping in a new place? Lots of people do. And now researchers from Brown University in Rhode Island think they know why. They found that one-half of the brain "remains more awake" than the other half when people are trying to sleep in a new place.

    The sleep findings were reported in Current Biology by Brown University. In their report, the researchers said many people report that they have a harder time sleeping the first night at a hotel or other places outside their home. They call it "first-night influence". "In Japan they say, 'If you change your bed, you can't sleep,'" said Yuka Sasaki, one of the report's writers. "You don't sleep very well in a new place. We all know about it."

    The researchers measured brain waves (测量脑波) for 35 volunteers over two nights in a laboratory. The two nights were a week apart(间隔).They found during the first night the left half of the brain was more active than the right half. This was during the first deep-sleep period, the researchers said.

    Sasaki said a lot of questions remain.

    Researchers did not keep measuring brain waves all night long. So, they don't know if the left half keeps "watch" all night, or whether it" works in shifts (轮换) with the right half later in the night" .They also do not know why the brain activity, at least during the first period of deep sleep, is always on the left half.

    For some, this research may be calming. It is good to know that our brain is "looking out for us" in a new place. But it may not help with sleep. That brain activity, at least according to this new research, makes it harder to get the sleep people need to wake up well rested in the morning.

    It's 21:00 in Beijing now. Let's look at what the four students are doing.