健身房里的跑步机太受欢迎了，我经常要排队才能用上。

The ___treadmills at the gym are so popular that I often have to wait in line to use one.

每天重复同样的工作让他感觉像在跑步机上，毫无新意。

Doing the same job every day makes him feel like he's on a ___treadmill, with no novelty.

古代的磨坊使用人力的踏车来带动石磨。

Ancient mills used a human-powered ___treadmill to turn the grinding stones.