Taking away a city's rubbish is a big job. Every day tracks come into a city to collect it. Most rubbish is made up of things we can't eat or use. If we kept these things we would soon have a mountain of rubbish.

    In some cities the rubbish is collected and taken outside of city to a dump. Often the city dump is placed where the ground is low or there is a big hole. The kitchen rubbish is broken into small pieces and sent into the sewage system. The sewage system takes away the used water from toilets, bathtubs and other places.

    To keep mice and flies away, some earth is used to cover the newly dumped rubbish. Later, grass may be planted on the rubbish-filled land. Finally, a house or a school may be built there, and then you'd never know that this had once been an old rubbish dump.

    In other cities the rubbish is burnt in special places. The fire burns everything but the metal. Sometimes the metal can be used again in factories where things are made of metal. The food parts of rubbish are put in special piles where they slowly change into something called humus, which looks like black earth. It is rich with the kinds of things that feed plants and help make them grow.

    On May 17, 2009, according to the plan, Mike Good and I would take a space walk to the Hubble Space Telescope to repair an instrument. The power supply on this instrument had failed, so it could no longer be used. I would be the person doing the repair and Mike my assistant.

    Working in space is more difficult than you can imagine. As there is no gravity, you can't stand and any slight push can result in tragedy -you can be pushed into space, never be back.

    We got to the telescope. Before we could replace the power supply, we would have to remove from the telescope a handrail fixed with four screws. Having taken out the first three, I found the fourth stripped. I realized that the handrail would not come off, which meant we could no longer be able to replace the power supply and repair that instrument, which meant scientists could no longer look at the universe and find life on other planets.

    I tried all kinds of things, and nothing worked. Then Houston, the control centre on the earth, called up and told me to use the tape to tape the bottom of the handrail and pull it off the telescope. They said it was going to take about 27 kilograms of force for me to do that.

    I knew what it meant: The handrail could be completely pulled off and the safety tether might break, and I might therefore be pushed into space.

    Mike was next to me in his space suit but he could not take over my role. I turned and looked into the cabin where my five crewmates were, and nobody in there had a space suit on. However, I knew they were all looking at me. "Come on Mass, we are all behind you." The telescope must be repaired.

    "Bam!" The handrail came right off. The rest of the walk went well. We finally got the new power supply in. They tried it; turned it on from the ground. The instrument came back to life.

    At the edge of darkness, after about eight hours, I turned around and saw the Earth from our altitude at Hubble, 568 kilometers up. I saw the huge round pure blue globe home planet. It's the most beautiful, magnificent thing I've ever seen. It's like looking into heaven. It's paradise.

    In earliest times, men considered lightning to be one of the great mysteries (神秘的事物) of nature. Some ancient peoples believed that lightning and thunder were the weapons (武器) of the gods.

    In reality, lightning is a flow of electricity formed high above the earth. A single flash of lightning 1.6 kilometres long has enough electricity to light one million light bulbs (灯泡).

    The American scientist and statesman, Benjamin Franklin, was the first to show the connection between electricity and lightning in 1752. In the same year he also built the first lightning rod (避雷针). This device (装置物) protects buildings from being damaged by lightning.

    Modern science has discovered that one stroke (闪击) of lightning has a voltage (电压) of more than 15 million volts (伏特). A flash of lightning between a cloud and the earth may be as long as 13 kilometers, and travel at a speed of 30 million meters per second.

    Scientists judge that there are about 2,000 million flashes of lightning per year. Lightning hits the Empire State Building in New York City 30 to 48 times a year. In the United States alone it kills an average (平均数) of one person every day.

    The safest place to be in case of an electrical storm is in a closed car. Outside, one should go to low ground and not get under trees. Also, one should stay out of water and away from metal fences. Inside a house, people should avoid open doorways and windows and not touch wires or metal things.

    With lightning, it is better to be safe than sorry?

    Scientists in Britain and the United States have made a new kind of enzyme(酵素) that eats plastics(塑料). With its help, plastics can be turned into smaller parts and go away quickly.

    Scientists believe that, in the future, it could solve the problem of plastic pollution.

    The enzyme is able to break down PET, a form of plastic. PET was first made in the 1940s and is now widely used to make plastic bottles. It can remain in the environment for many years and pollute large areas of land and water. So it has always been a headache to deal with the waste from PET and other plastics.

    The researchers made the discovery(发 现) while examining the structure of a natural enzyme in Japan. They found that the natural enzyme was helping to break down PET plastics. So, they

decided to make small changes to the enzyme by adding some amino acids(氨基酸). It made the natural enzyme's plastic-eating abilities work faster and better.

    John McGeehan, one of the lead researchers, said, "We've made an improved enzyme. It's better than the naturl one. And we are trying to make more improvements to it." He went on."

    The enzyme is not harmful to humans or animals, and it is friendly to the environment. So we are considering putting it into wider use."

    The team is now trying to make the enzyme break down PET in large quantities(大量的). "We'll see that the plastic pollution may be stopped with this technology. However, there is still a long way to go," John McGeehan added.

Some people around you look so cool and happy, but you often feel lonely. Or the friends you have do not really understand you, and that makes you feel lonely too. So what can be done when you have this feeling?

Understand people's differences

Not everyone has to do things the same way or behave the same way. Find people who have the same feeling. That is always a good basic for the friendship. You can take part in activities outside school like sports, art classes and dancing classes. There you can have more chances to find people who have the same interest as you.

Develop your friendship

Friendships do not just happen, and they need work. Phone your friends once in a while. Being there when they need you means that they will do the same for you.

Accept others' invitations

Even if someone invites you to a party, you never know who else will be there. Laughing and playing together could start a new friendship.

Start a club

Make more friends by starting a club. Going camping together or regularly (有规律地) going to the movies doesn't take much time.