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 best way to teach your children to live a green lifestyle is to live that green lifestyle yourself. When kids see you picking up rubbish from the park, they see value(价值)in keeping public places clean Use these tips to introduce your children to green living：

    Use public transport. Use the car only when necessary; at other times, take trains and buses with your children.

    Ask for their help. Younger children often love grown-up activities. So have them carry a small bag of food waste to the bin, or let them help separate(分开)your recycling. Older children may want to take part in the activities like cleaning up the neighbourhood and organizing the daily recycling If they're not very interested, make environment-friendly activities a family-time priority (优先事项)

    _________________________ Petting farms for younger kids may help prevent(防止)farm animals from becoming something that they see only in books or on television. Many people believe that wild animals shouldn't be kept in any kind of zoos, but they do offer a valuable educational and conservation(保护)lesson. So if you want to visit a zoo, find a zoo that provides its animals with as natural an environment as possible

    In some science fiction movies, evil robots refuse to die, no matter how hard people fight back.

    Now science fiction has become science fact. For the first time, scientists have made a robot that can take a beating (挨打) and keep on going. Scientists from Cornell University made the robot, which looks like a spider with four legs.

    Until now, even the most advanced (先进的) robot was almost certain to break down when it was damaged. That is because its computer inside simply doesn't know how to make the machine work after its shape has changed.

    To deal with this problem, the scientists put eight motors (发动机) and two sensors (传感器) that read how the machine is working. They all give signals to the machine's software. Using this information, the computer can then figure out the machine's shape at any moment.

    The new technology is a big advance in robot-making, scientists say, and it's far from scary. It may someday help scientists create better artificial (假的) arms and legs and give new freedom to people who lose them. It might also help scientists understand how people and animals figure out their own sense of place in space.

    "It has been difficult to design robots that can work well when the environment changes or when it's damaged," says Olaf Sporns of Indiana University in US. "With this work, we are nearer to solving this problem."

    Everyone knows the strange feeling of your fingers wrinkling up (起皱) when they're wet. Sometimes when in water, it seems as if your hands have aged 30 years in a second. But is this an accident? Or is it something that nature has built into our bodies?

    Scientists at the University of Newcastle in the UK recently did a test. They asked people to pick up things (some wet and some dry). And take them from one place to another. Some people did this with dry hands, while others had to leave their hands in water for 30 minutes first so that their skin was wrinkled. The study found the second group with wet hands had an advantage when carrying things that were also wet.

    The scientist Tom Smulders said that "this wrinkling of our fingers in wet conditions could have helped with gathering food from wet vegetation or streams". Wrinkling happens when blood vessels contract (血管收缩) and pull the skin back.

    A long time ago, humans lived a very difficult life in a brutal world, where the smallest advantage could make a huge difference. Having wrinkled skin might have helped people catch fish. This would help them get through the winter. These humans would then have had an advantage. Their genes would be accepted by natural selection.