Paper was improved by a Chinese man called Cai Lun in 105 AD. In the 11th century, China began to use paper money. 【小题1】 . At that time, people made paper from the wood of a special kind of tree.

【小题2】. And more and more paper is used. You know, 17 trees are needed to make one ton of paper. And it takes more than 10 years for a tree to grow. It is clear that there will be fewer and fewer trees left on Earth soon. Therefore, 【小题3】.

Now we know it is important not to waste paper. 【小题4】 ?   First, we can use both sides of every piece of paper. Second, we can put drinks in bottles instead of paper boxes. 【小题5】. We can also use handkerchiefs instead of tissues. Last, we can reuse envelopes(信封). We can use fewer paper shopping bags by reusing them as well.

The Beijing 2022 Winter Olympics was a great success. China has kept the promise to hold a green Olympics. It took more than six years to prepare for the Games. In this process, the designers put the idea of green Olympics into every part. They integrated green Olympics with the city and its surroundings (环境). Many green actions made it possible, like providing environmentally friendly smart beds, using a large number of new energy cars, supporting sporting places with 100% clean energy and reusing rain and snow water.

Take making ice as an example. China didn’t use R507, a common material to make ice, because it isn’t friendly enough to the environment. Through 18 months’ hard work, China independently developed the CO₂ direct cooling technology.

A net of tubes (管道) runs under the ice. High-pressure liquid (液态) CO₂ goes through them to create heat (热) exchange. The CO₂ evaporates (蒸发) under the ice surface. The evaporation takes in heat and turns water on the surface into ice. And the CO₂ goes into another circle. This technology helps to make ice better and faster. And above all, it is much greener because there’s no new CO₂ produced. Among all the 15 ice sporting places in the Winter Olympics, 7 used the CO₂ direct cooling technology to make ice. As a result, much less pollution was caused.

The Beijing 2022 Winter Olympics is the first to truly achieve carbon neutrality (碳中和), and it has set new standards in green technologies. Some newspapers say China has made great contributions to the world's environmental protection and green development.