Why so many wheels compared to like a four wheel roller skate or roller blade or something?

为什么有这么多轮子，而不是像四轮旱冰鞋或滚轴刀片之类的东西？

In the video, they test out some roller blades.

在视频中，他们测试了一些旱冰鞋。

Did you bring your roller blades?

- 你带了溜冰鞋吗？

A skate park is a place where you can bring your skateboard, your roller blades.

滑板公园是您可以携带滑板和旱冰鞋的地方。

I actually hold an unofficial land speed record for a rocket bike and roller blades while wearing a rocket pack.

实际上，我在穿着火箭背包时保持着火箭自行车和旱冰鞋的非官方陆地速度记录。

To lag behind is to move slowly behind other moving objects. The girl on roller blades laged behind the little girl on the bicycle.

behind是指在其他移动物体后面缓慢移动 穿旱冰鞋的女孩跟在骑自行车的小女孩后面。