There is little doubt that house cat first developed naturally from ancient wild cats. The cleverest relative is the America wild cat which still lives in Africa today. This is understandable because the first house cats came from Africa.

    Cats first started to live around people in Egypt about 6,000~7,000 years ago. From Egypt, cats started to move around the world. This is about the same time that Egyptians began storing grain(谷物）in buildings. Scientists used to believe that people tamed cats to catch mice and protect the grain. However, cats don't like to be told what to do! Now, scientists believed that cats followed the mice and learned to accept people. Finally, some of the cats began to grow comfortable around people, these were smaller cats that needed protection. As these cats and people got used to each other, then they moved in together. Around 5,000 years ago, cats started to live with people.

   Soon cats were in Greece, then the Middle East and China. They moved along Egyptian business roads keeping away mice and keeping people around them. After the Romans came to Egypt, they also accepted the cats and brought them to Europe. These cat likely bred(繁殖） with other cats to form the many kinds of house cats we have today.

    Cats are relatively recent house animals. House cats still have a lot in common with their wild relatives. Cats sleep a lot to save energy just like wild cats. They will often get food at night as well. House cats are generally peaceful and friendly, but be careful! If a cat feels it is in danger, it will fight back—just like a wild cat.

     A serious earthquake can be a terrible experience, and it is easy to forget safety measures(措施) in disorder(混乱). Fortunately, most earthquake safety measures are common sense, but if you forget everything else, re­member the following instructions: drop, cover, and hold on. Also, most of earthquake deaths hap­pen after the earthquake, so remember that the danger does not end when the shaking does!

     If you stay indoors during an earthquake, move away from unsupported areas and windows. Try to get under a doorway or another area of the building which is held up by strong beams(梁).  Stay under a table or desk only if it is very strong. Do not rush to lifts, because it is far safer to stay where you are. Cover your head with your arms around it and curl (蜷缩) into a ball, and wait for the shaking to stop.

     If you stay outdoors during an earthquake, move to an area which is as open as possible. Don't move to build­ings, electric poles and other objects which may fall during an earthquake and injure you. Protect your head and stay low to the ground till the shaking ends and it is safe to move.

     After an earthquake, many buildings are less strong, although they appear safe. If you stay indoors, move people from the building quickly and help disabled or injured people. Once outdoors, move well away from the building so that if it falls down, you will not be injured. Wait till public safety officials an­nounce that it is safe to stay indoors.

     By planning ahead and keeping calm during an earthquake, you can greatly increase your chances of survival(生存) without injury.

   The population of the Earth is growing faster. It is important that we look after the Earth. We need it! The Earth gives us a lot of things. We also give the Earth a lot, but some of the things are not good.

   In nature, when something dies, other animals and plants get food from it. Every animal or plant gives food for other animals or plants. However, animals can't get food from many of the things that we "give" the Earth. Animals and plants can't eat metal, plastic and glass. These things will stay in the ground for many, many years.

   Some rubbish is very dangerous for plants and animals. In some places, many animals live together. One animal makes food for many more animals. If we put rubbish and chemicals in the water, the plankton(浮游生物) can die. If there isn't any plankton, many animals have nothing to eat.
   So what can we do? Don't leave any rubbish in the countryside! Don't make so much rubbish!

    Sheridan is a town in Indiana, USA. There are lots of trees near the public schools in the town. Their leaves turn sunlight into energy（能量）.

    In Sheridan, the sun not just provides energy for plants. It keeps schools running, too. The schools use solar panels（太阳能电池板） to turn sunlight into energy.

    The science behind solar energy is not new. But Sheridan Community Schools is the first school district(学区) in Indiana to be completely solar-powered. The district finished putting in solar panels for all three of its schools in 2016. Some of the panels can turn to follow the sun across the sky.

    In 2008, fewer than 1. 000 schools used solar power. By 2014, there were 3, 727 schools with solar panels in the USA. These numbers come from a report by the Solar Foundation. Roxie Brown, a program director there said that the number of schools with solar panels has continued to go up since 2014.

    Solar energy has some advantages over other energy sources(来源). Sunlight is a renewable source, which means it won't run out. Solar panels don't harm the environment. Also, sunlight is free. So by using solar power, schools can save money on energy costs.

    Brown thinks more schools should run on solar energy. "The sun is Earth s energy source," she says. "We're trying to make it the energy source for our houses cars and schools, too."

    But using solar energy isn't always easy. Solar panels can be expensive to put in. The panels also take up space. But for many schools, going solar is worth it.

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How to live well on our own As middle school students，we really need to know the importance of living well on our own.