Most of us spend a third of our lives sleeping. Scientists have been studying the brain to learn what happens while we sleep. Scientists tell us that there are four stages(阶段)of sleep. During each stage our brain behaves differently, and so does our body. Each stage is marked by changes in the pattern of brain waves, which can be recorded by machines.

    In the first stage, we drift off to sleep. Our muscles(肌肉)begin to relax. Our heartbeat and breathing slow down. Body temperature and blood pressure(压力)begin to drop. Stage-two sleep is a time of small, fast brain waves. Our eyes move quickly from side to side as if watching a movie. This is known as rapid eye movement, or REM sleep. During REM sleep, dreaming takes place. In stage three the brain wave becomes slower again.

    Within about 45 minutes after falling sleep, we progress into the fourth stage – deep sleep. As this happens, our brain sends out slower but larger brain waves. This is the most restful kind of sleep, but it is also the time when sleepers are most likely to change positions or sleepwalk. After deep sleep we return to stage two. As the hours pass, we repeat the sleep cycle four or five times. Then we wake up.

Do you know the "four treasures of the study" in ancient China? They are the writing brush, ink, paper, and the inkstone (砚台) . Among all the inkstones, the Chengni inkstone is one of the most famous inkstones and is widely loved. 

The Chengni inkstone first appeared during the Western Han Dynasty, but the skills of making it were lost during the late Ming Dynasty and early Qing Dynasty. Thankfully, today the traditional skills have been revived (复习) with the help of Lin Yongmao and his son Lin Tao. 

In 1984, Lin Yongmao began working at the museum in Xinjiang, Shanxi Province. There he read some books about the Xinjiang Chengni inkstone, and then decided to revive the lost skills. 

It was easier said than done. It took the father and son two years to find proper materials to produce the Chengni inkstone. That was just the first step. After failing many times, they finally succeeded in making two Chengni inkstones in 1991. Three years later, their Chengni inkstones won a gold prize at an expo (博览会) on China's famous inkstones. 

But the father and son didn't stop there. While improving the skills of making the Chengni inkstone, they set up a workshop in the hope of passing the skills on to young people. They also worked with universities and colleges to make the Chengni inkstone more popular. At the same time, Lin Tao has created special Chengni inkstone products and brought them to competitions at home and abroad to expand the influence of the Chengni inkstone. 

Every year，TIME magazine puts out its list of best inventions. They change how we live，work

 Between June 3 and 4, 2024, the Chang'e 6 lunar probe(月球探测器) showed our national flag on the moon. This is the first flag of any country to fly there!

 The flag uses very cool technology (技术). It is made of Xuanwu rock. You can often see this kind of rock on Earth. People often make the rock into floors and roads. The rock for making the flag comes from Hebei. Scientists first crushed (碾碎) the rock. Then, they made it into very thin threads (线), even thinner than your hair! Finally, they put these threads together to make a flag about the size of a piece of A4 paper.

Although the flag is made of rock, it is not heavy. It's just a little heavier than four ping- pong balls. The flag could stay there for over 10,000 years, said Zhou Changyi, one of the scientists who made the flag.

How do people from all over the world spend their free time? Let's have a look.