Long ago, as people got older, there was something wrong with their teeth and it would be very painful. To avoid toothache, they had their teeth pulled out.

Later people learned that cleaning their teeth was important, but they didn't have toothpaste (牙膏) at that time. They used lemon juice (柠檬汁), salt or other things to clean their teeth.

About 100 years ago someone finally created a kind of cream to clean teeth. Not long after that, the toothpaste tube (管子) was invented, so people could press the toothpaste right onto the toothbrush! Tooth brushing became popular during the World War I. The army gave brushes and toothpaste to all the soldiers, and they learned to brush teeth twice a day. At that time toothpaste tubes were made of metal. Today they're made of soft plastic and are much easier to use!

Today there are plenty of toothpaste choices: lots of colors and tastes to choose from, and some kinds of toothpaste are made just for children. When you're choosing a kind of toothpaste, make sure it has fluoride (氟化物). Fluoride makes your teeth strong and healthy.

There are many inventions that have caused great changes in the world. Here is a short introduction of the maglev train(磁悬浮). The history of the maglev train started in the beginning or the 1900s. The American Robert Goddard and the French Emic Bachelet came up with the idea of frictionless(无摩擦的）trains. But scientist didn't succeed in making it at that time.

About 60 years later, the Japanese started their research on maglev transportation. After many years of experiments, the Japanese began to build their first test line 7km in 1975, and finished it in 1977. Many test runs started in July 1977 with a speed of 517 km/h. In 1990, Japan built the Yamanashi Maglev test line. This test line was 42.8 km long and the first running test was held in 1997.

The Germans also started research on the maglev train in the early 1970s. It took them ten years to make the first track( 轨 道 )model. In 1993, the longest nonstop test running was 1,674 km. That same year the speed reached 450km/h.

China finished a 30-km-long maglev train line in Shanghai in 2003. This is the first commercial ( 商业 的 ）maglev train line in the world. Although this project cost over l billion dollars, we should feel proud of it.

In early 2024, four students from Diocesan Boys’ School in Hong Kong set a new Guinness record by creating the world’s smallest humanoid (人形的) robot. The robot stands at a height of 141millimeters, shorter than a pen.

According to the rules of the Guinness World Records, the robot must be able to show clear joints (关节) between its shoulders, elbows, and knees and walk like a person. However, it was not an easy task to make the small robot move its body with the narrow space between the robot’s joints. Moreover, the original battery (电池) they used was too large for such a small robot, so they settled for a smaller 7.4 V lithium-ion battery.

Apart from breaking the world record, the low-cost robot can also serve as a STEAM (science, technology, engineering, arts, and math) learning tool. Before this creation, the robots available for STEAM education in the market were quite expensive.