Why do plants grow in some places and not in others? Why does some land have so many plants growing on it, while other land has almost no plants growing on at all?

    To grow, plants need some things. One is warmth. In very cold places, almost nothing grows, Plants also need water. In very dry parts of the Earth, only a few unusual plants can grow. That's why dry deserts(沙漠）almost don't have trees or grass.

    Plants must also have a place in which to put down their roots（根）and grow. They find it difficult to grow on hard land. The town is on hard land. The plants here can only grow in the soil（土壤）between the cracks of the stones.

    Another thing plants must have before they can grow is food.

    What will happen if we try to make things grow on the sandy（有沙的）beach? A few plants, such as beach grass, will grow in sand, but most plants won't. Even if（即使）the weather is warm enough and we water the plants each day, many of them will die because the sand on this beach has almost no food for plants.

Where does the wind come from? What makes the wind move(移动) all the time? Scientists tell us that it is the sun. That makes air move, and makes it blow(吹). When the sun shines on the earth, it makes the earth hot. Then the earth makes the air hot. When the air becomes hotter, it also becomes lighter(更轻). The light air goes up. Cool air comes into take the place of（代替） the hot air. The hot light air goes up higher and higher until it becomes cool. Then it comes down again, and then the earth makes it hot again, and it has to go up. When the air move, it has wind.

    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.

    If you travel by air across the center of Africa or South America, you fly over forests for thousands of kilometres．These great forests are the seas of trees．They are full of thousands and thousands of different kinds of plants and animals．However, the world's forests are getting smaller all the time．We are cutting down the trees because we need wood, and we need more farmland as well．Some people say that there will not be any forests like these left in 20 to 30 years．What will happen if they disappear? If we cut down our forests, a lot of plants and animals will disappear from the world, in a lot of places the new farmland will soon look like the old deserts, for example, crops will not grow there．What's worse, it will not rain very often, and the weather will get very hot．Perhaps the climate of the world will change, which will be dangerous for everyone in the world．That is why we must take care of our forests．

    The tiger is the largest wild cat in the world. It is the king of animals. Tigers often eat 5kg of meat for a meal. Tigers can see very well in the dark. They often hunt at night. Sometimes they can eat 27kg of meat at one night. Most members of the cat family dislike water, but tigers enjoy water. They are good at swimming. Many animals live in groups, but tigers live alone（单独地）, except for（除了） mothers and their young babies. A mother tiger usually has two or three babies at one time. She takes care of them by herself.

    There were eight kinds of tigers in the world, but three of them died out（灭绝）. There are only about 3200wild tigers in the world now because people kill tigers and destroy the places where they live.