There is little rain in desert. Because deserts are so dry, they have no "quilt" to help stop the soil from going away. As a result, they may get very hot during the day with the sun shining, but don't hold the heat overnight. Many deserts can quickly get cold once the sun goes down. Some deserts can reach temperatures of over 100 degrees F during the day and then drop below freezing (32 degrees F) during the night.

The largest hot and dry desert in the world is the Sahara Desert in Northern Africa. The Sahara is a sandy desert with great sand hills. It covers over 3 million square miles of Africa. Other large deserts include the Arabian Desert in the Middle East, the Gobi Desert in Northern China and Mongolia, and Kalahari Desert in Africa.

Animals that live in the desert are also used to needing little water. Many get all the water they need from the food they eat. Other animals keep water that they can use later. The camel stores up fat in its hump while other animals keep something they need in their tails.

Only certain types of plants can live in the terrible environment of the desert. You won't see a lot of tall trees in the desert. Most plants have a way to keep water in their leaves, or trunks so they can live a long time without water.

Now deserts cover around 20% of the world's land, but they are growing. This is called desertification and is caused by different reasons including human activities. The Sahara Desert is growing larger and larger each year. What should we do with it ?

    Height is just one of the thousands of features your genes decide. In fact, because you have two parents, your genes provide you a height that usually lands somewhere between the height of each parent. If both your parents are tall, then most probably you will be tall, too, but if you have questions about how tall you're going to be, ask your doctor if he or she can help you find it out.

    But genes don't decide everything. For example, eating an unhealthy diet can keep you from growing to your full potential(潜力). Getting plenty of sleep and enough exercise will help you grow to the expected height.

    No doubt you're wondering how fast you should grow. It depends. There's no perfect or right answer. Generally speaking, kids grow about 2 inches (6 centimeters) a year between age 3 and the time when they start puberty (when your body starts changing and becoming more grown up).

    Your doctor will know how your growth has been going over the years. Two centimeters here and 2 inches there are not nearly as important as the height you're at now, how you've been growing up to this point, and what other changes your body may be going through.

    Don't be scared if you seem to have grown a lot in a very short time. Everyone has a growth spurt（高峰）during____The age for starting puberty is about 10 for girls and about 11 for boys. But it can be earlier or later —between 7 and 13 for girls and 9 and 15 for boys.

    You'll usually begin to notice that you're growing faster about a year or so after your body starts to show the first changes of puberty.

    Every day there is less and less space on Earth for rubbish. Yet every day we make more and more rubbish. What can we do? We can recycle some of our rubbish. Recycling means that the rubbish will be made into something that can be used again.

    Recycling helps Earth. And it saves space in rubbish dumps. Half of everything that we put into landfills could be recycled instead. In fact, most things made of paper, metal, glass and plastic can be recycled.

    Paper can be broken into small pieces and made into new paper. Steel and aluminum cans(金属雄)can be melted down(熔化)and made into new cans. The same is true of glass bottles. This can be done over and over again. Recycling doesn't take as much energy as making these things the first time. So we can use less of Earth's fuel resources.

    Plastic can be melted down, too. Then it can be formed into park benches, playgrounds and so on. Some people call plastic the "wood" of the future. Things made of plastic will last about 400 years-even if they stay outside in the weather. No wood can do that!

    Like you, plants need good things like food, water, and minerals in order to grow. Usually they get these important nutrients(营养) from the rich soil(土壤) in which they're planted. But there's another way to grow plants that doesn't use soil. It's called hydrogenic gardening.

    "Hydrogenic" means "working with water." In a hydrogenic garden, plants grow with their roots in water, not in dirt. The water is filled with special food for the plants that gardeners have carefully measured and prepared.

    Hydrogenic plants grow quickly. In ordinary gardens, plants need time and energy to grow long roots that search the soil for food and water. In a hydrogenic garden, plants can use their energy to grow tall instead. And because there is no soil, there are no weeds and few insect pests(害虫). Gardeners don't need to spray(喷洒) plants with dangerous chemicals. Both the plants and the environment stay healthy. 

    Scientists hope that, one day, hydrogenic gardens may be able to help hungry people all over the world grow enough food-even in countries that have bad soil, or weather that is too hot, too cold, or too dry. And astronauts hope to take hydrogenic gardens with them to the spaceship they fly to Mars, so that they will always have fresh vegetables, and the fun of growing a garden without dirt. 

    Americans think much about time. From childhood they learn to {#blank#}1{#/blank#} time. They are taught to be on time to go to school, to work and to do everything. When they are having a good time, they time goes easily. When a person is dying, they say he is living on borrowed time.

    Time is money. Time is knowledge. Time is {#blank#}2{#/blank#}in America. A working American has to work hard for eight hours a day or forty hours a week. This is the working time. In his free time, he also works hard for more money. Even on Saturday and Sunday he also works hard as {#blank#}3{#/blank#}. In the street you can hardly see a man walking{#blank#}4{#/blank#}. They walk very fast. In fact, they are running.

    They love time because time can bring them money and lots of things.{#blank#}5{#/blank#}sometimes they also hate time, because they feel they have become servants of the clock.

In China, different people have different 1 to enjoy themselves. They also have 2 own ideas about how to pass time. 

For most children, their lives are3 studies in school. They have little free time. After school, they want to put aside their 4 and go out to play. 

Some old people get 5 early in the morning. Then they often go to parks to exercise. It helps them6 more friends. In the evening, they would prefer to stay at home 7 have a rest. 

 As for young people, they enjoy having a trip on weekends to8 . They go to the 9 to camp. They usually spend one or two days on mountains. Then on Sunday evening, they start their way back home. 

Everyone wants to keep10 .