Hundreds of years ago, life was harder than it is today. People didn't have modern machines. There was no modern medicine, either.

    Life today has brought new problems. One of the biggest is pollution. Water pollution has made our rivers and lakes dirty. It kills our fish and pollutes our drinking water. Noise pollution makes us talk louder and become angry more easily. Air pollution is the most serious kind of pollution to all living things in the world.

    Cars, planes and factories all pollute our air every day. Sometimes the polluted air is so thick that it is like a quilt (被状物) over a city. This kind of quilt is called smog.

    Many countries are making rules to fight pollution. Factories must now clean their water before it is thrown away, and they mustn't let dirty smoke go into the air.

    We need to do many other things. We can put waste things in the dustbin and do not throw them on the ground. We can go to work by bus with our friends in the same car. If there are fewer people driving, there will be less pollution.

    Rules are not enough. Every person must help to fight pollution.

    People and animals live in the same world. We should keep the balance（平衡）b{#blank#}1{#/blank#} people and animals. If the balance is destroyed，there will be bad result to both people and animals. Wild animals are friends of people. We have to p{#blank#}2{#/blank#} them， or there will be no wild animals in the future. Now we know that there are  n{#blank#}3{#/blank#} 2，000 nature reserves(自然保护区) in China

    There is a black and white animal l{#blank#}4{#/blank#} in China. It is always known as the national treasure(国宝) of China. Everyone knows it is c{#blank#}5{#/blank#} Giant panda. Now there are f{#blank#}6{#/blank#} pandas than before. Most of them live in Sichuan and Gansu Provinces. There are also some other rare animals in China. H{#blank#}7{#/blank#}， the n{#blank#}8{#/blank#} is becoming smaller and smaller than before. So people should try t{#blank#}9{#/blank#} best to help these animals. They are in d{#blank#}10{#/blank#} of disappearing from the world.

    When you look at the sky at night, the Moon looks bigger than the stars. Actually (实际上), the Moon is much smaller than the stars and the Sun. It's much smaller than the Earth. But the Moon is much closer to us than any star. That is why it looks so big. If you hold a coin close to your eyes, it looks big. If you look at it across the Moon, it looks small.

    The Moon moves around the Earth. It makes one trip in about four weeks. The Moon looks flat to us. But it is a round ball, like the Earth.

    People once thought the Moon had fire (火) on it. They thought the fire made it bright. Now we know the Moon is like a mirror. It gets its light from the Sun.

    Our sunlight comes from the Sun, too. What is the Sun? The Sun is a star. The stars we can see have their own light. There are many big stars we cannot see. Their light has burned out. Others are still bright, but they are so far away that we cannot see them. The Sun looks bigger and much brighter than other stars in Galaxy because it is the nearest of all stars. The Sun and the other stars we see are very hot, but the air around us saves us from the heat of the Sun.

    The Sun gives us light and warmth (温暖). It makes plants grow and turns leaves green. It makes life possible on the Earth. It is a life giving star.

    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. 

    Mobile Apps are part of our daily life. Here are some of the most popular Apps.