Please wear a helmet when riding a bicycle.

骑自行车时请戴上头盔。

I saw the postman riding a bicycle on the street.

我看到邮差在街上骑自行车。

When riding a bicycle, please keep right for safety.

骑自行车时，请靠右，以确保安全。

Riding a bicycle is an eco-friendly mode of transportation.

骑自行车是一种环保的交通方式。

Riding a bicycle is a common way to travel by non-motor vehicle.

骑自行车是一种常见的非机动车出行方式。

The speed per hour of riding a bicycle is about 20 kilometers.

骑自行车的时速大约是20公里。

He prefers riding a tricycle over a bicycle because it feels safer.

他更喜欢骑三轮车而不是自行车，因为感觉更安全。

Riding a bicycle is a good way of maintaining personal fitness and doesn't harm your health either.

骑自行车是保持个人健康的好方法，也不会损害你的健康。

Is she riding a bicycle?

她正在骑自行车吗?。

It felt more like riding a bicycle than walking.

它更像骑自行车，而不像步行。