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    Air pollution is one of the most common types of pollution in the world nowadays. It is quite serious in many places, especially in big cities. It can do great harm to our environment such as making the earth warmer, causing acid rain or destroying the ozone layer. As for human beings, air pollution causes all kinds of breathing problems.

    There are several reasons for air pollution. Firstly, many cities have a lot of factories and there we need to make food, clothing and other things. Every year these factories pour millions of tons of smog into air. Secondly, power factories can also give out harmful air. For example, in 1986 there was a bad accident at a nuclear power station in Russia. A cloud of radiation crossed the whole Europe. It is said that 125,000 people died in Russia as a result of illnesses caused by this accident. Thirdly, there are more cars in cities now. Once they are out in the streets, they will take in fresh air and give out dirty gas. Besides, smoking cigarettes also makes air pollution worse as will as damaging(损害) our health.  

    In 1826, a Frenchman named Niepce needed pictures for his business .But he was not a good artist .So he invented a very simple camera. He put it in a window of his house and took a picture of his garden .That was the first photo.

    The next important date in the history of photography was in 1837. That year, Daguerre, another Frenchman, took a picture of his reading room .He used a new kind of camera in a different way. In his picture you could see everything very clearly, even the smallest thing. This kind of photo was called a Daguerreotype.

    Soon, other people began to use Daguerre's way. Travelers brought back wonderful photos from all around the world .people took picture of famous buildings, cities and mountains.

    In about 1840, photography was improved .Then photographers could take pictures of people and moving things .That was not simple .The photographers had to carry a lot of films and other machines. But this did not stop them, for example, some in the United States worked so hard. Mathew Brady was a famous American photographer. He took many pictures of great people .The pictures were unusual because they were very lifelike.

    Photographers also became one kind of art by the end of the 19th century. Some photos were not just copies of the real world .They showed feelings like other kinds of art.

    In recent years, a number of Chinese technological innovations (科技创新) have been making waves around the world. Among them, four stand out. They are known as "four new great inventions of modern China. They have made our daily lives more convenient.

    High-speed trains

    China created its first high-speed railway line in 2008. Since then, the number of passenger trips has grown by over 30 percent every year. By 2016, more than 5 billion trips had been taken on China's bullet trains(高铁), according to Xinhua News Agency.

    China is currently working on the next-generation bullet trains that will have a top speed of 400 kilometers per hour. By 2020, one-fifth of the country's 150, 000-km railway network will be used by high-speed trains. This network will link more than 80 percent of major cities across China, said Xinhua.

    Mobile payment

    Mobile payment is turning China into a "cashless society" led by the third-party payment companies like Alipay. For example, instead of paying by cash, customers now pay for goods simply by typing a short password into Alipay app on their mobile devices.

    Users can also pay their bills through Alipay, such as their water and electricity bills. Alipay also supports cross-border(跨境的)online and in-store payment, which allows users to buy things on international websites and apps.

    Shared bikes

    Shared bike services started in Western countries. But China has surprised the world with how

quickly it has adopted dockless(无柱的) shared bikes.

    Unlike traditional bike-sharing method, dockless bikes allow users to simply pick up or park a bike on the street through GPS and smartphone app.

    To unlock a bike, you just need to scan a QR code on a shared bike with a smartphone app. After you finish riding, you can park it at available parking areas, lock it and pay for ride through mobile payment services.

    Online shopping

    With around 751 million internet users, China has been the world's largest and fastest-growing line shopping market.

    Online shopping now accounts for 15. 5 percent of total retail sales in China, according to Xinhua. Thanks to lower costs and fewer licensing requirements(执照要求), it's easier for sellers

to open an online shop in China than a brick-and- mortar shop(实体店).

    It also helped to create jobs of rural areas. In 2016, online shopping created more than 20 million jobs in rural areas, with over 8. 1 million running their own online shops, said Xinhua.

    My parents often take me to the zoo at weekends. I like animals. I have many toy animals in my room. In the zoo I can see tigers, elephants, pandas and many other animals. Some animals are friendly, but some are not. Tigers, lions and snakes are dangerous. That is why they have to be in the cage. But I think it is terrible for animals to be in the cage.

    Tigers usually live in forests and mountains. They can run. They catch and eat small animals, but now they live in small rooms. They can only walk and sleep in the cages, and they want to go out. I feel sorry for them.

    I think my favourite animals are dolphins. I like watching them swim and jump. They can play with a ball. They can "walk" on the water! They are very friendly to people. They can help you when you fall into water and can't swim.