two revolving field method

例句：

1. 1.The car's engine is revolving at a high speed.
   汽车的引擎正在高速旋转。
2. 2. The wheel of the caris revolving around the hub.
   汽车轮子在轮毂周围旋转。
3. 3. The revolving door is opening and closing frequently.
   自动门开开关关频繁。