One day, a father and his son went to a kite flying festival. When they arrived, there were already many adults and their children playing in the park. When the son saw the sky filled with     1     in different shapes, he was excited and wanted to get one, too. His father agreed. So they went to a kite shop and     2     a beautiful one. With the string (线) in hand, the son started flying the kite. Soon, the kite was high up in the sky.     3    , the son said, “Father, it seems that the string stop the kite from flying higher. If we cut it, it will be free and fly even higher. Can you cut it?” The father didn’t reply, but just     4     the string. Suddenly, the kite began to go higher, which made the son much happier.

However,     5    , the kite was coming down slowly. They waited for quite some time, it fell onto the grass. The son felt upset and asked, “I thought that after cutting the string, the kite would fly higher. Why did it     6    ?” The father smiled and said, “The role of the string was not stopping the kite from flying higher, but helping it stay in the sky because the kite     7     can’t fly up. By using the string, you help the kite go up the right direction. When you cut off the string, it could not support the kite.

In our life, we may sometimes     8     there are certain things that are holding us back and stopping us from growing, but in fact, these might be the things that support us most. We can really grow up and become stronger by realizing the importance of these things.

Climate change is a big problem humans are facing. How can we deal with it? Reducing carbon emissions (碳排放) is important. But what if we could capture carbon dioxide (CO2) from the air and use it to do other things?

Recently, SpaceX founder Elon Musk said that his company is working on a new program. It’s going to take CO2 out of the air and turn it into rocket fuel.

It will not only be good for Earth, but “will also be important for Mars,” Musk said. The air on Mars is made up of 95 percent CO2. If we could turn CO2 into fuel, we could travel the long journey from Mars back to Earth in the future.

The idea may sound strange but it’s not totally crazy. There are already some technologies that might help with this. According to Di-Jia Liu, a chemist at the Argonne National Laboratory in the US, the carbon atoms (原子) in CO2 and the hydrogen (氢) atoms in water can be combined to make methane (甲烷) or ethanol (乙醇). They could be used as fuel. If we do this on Mars, energy from the sun might be used as a catalyst (催化剂).

The idea will also make space travel more eco-friendly. “If the CO2-based fuel could be used in a rocket launch, we could prevent 715 tons of CO2 from being put into the air,” said Stafford Sheehan from Air Company, a US company that focuses on CO2 collecting technologies.

More and more people like bicycling and it is no surprise. It’s fun, healthy and good for the environment. Maybe that’s why there are more and more bicycles on roads worldwide today. Bikes can take you almost anywhere, and there is no oil cost!

However, two centuries ago, when bicycles were first invented, they were used only for transportation. In the eighteenth century, people usually traveled by horse and wagon (马车). In 1817, an early “bicycle” was made in Germany. Its frame (车架) was made of wood. It didn’t have any pedals (踏板). People had to push with their feet. In the 1830s, the first bicycle was invented. Pedals were made for the bicycle. In the 1860s, Frenchman Pierre Miehaux and his son gave the bicycle a new look. In 1867, they brought the bicycle to the world Expo (世博会). Since then, the bicycle was more and more popular in Europe. In the 1870s, the front wheel was much larger than the back one. This made it very hard to ride. It was also very expensive. In the 1890s, bicycles with same-sized wheels came out in North America and Western Europe. They were much safer, cheaper and more comfortable.

In China there are shared bikes on the roads. They have saved us a lot of time during hurry situations, and on beautiful, clear days. However, bicycling is not easy in our city. There are no bicycle lanes (车道), and bikers have to travel next to cars in car lanes.