Different countries have different bicycle-sharing systems towards children. Chinese children are welcomed on the country's using bicycle-sharing systems at age 12. In Paris, 14-year-old children     1     (allow). The age minimums for US bicycle-sharing systems   are generally 16 or 18. Research shows children    2     do some exercise in the morning concentrate better in school. When more people ride bikes, air quality improves, aiding everyone's health. Having a bicycle also teaches responsibility and    3     (confident). People learn how to ride    4     (safe) on city streets and respect rules of the road. When   students are riding in the street , there’s a real ownership that they feel over their city. Of course, it's very important for riders to understand traffic rules.

The railway line     1    (connect) Beijing and Zhangjiakou, the co-host city of the Beijing 2022 Winter Olympics, is the world's first intelligent, high-speed railway. It     2    (go)into operation on Dec 30, 2019. The railway is 174 km long, with a maximum design speed of 350 kph. It reduces the travel time between Beijing and Zhangjiakou from over three hours to 47 minutes. The train is designed with an area to store snowboards, a device to secure wheelchairs and a mobile news center     3     passengers can watch live Olympic broadcasts.