flat jewel cylindrical hole for oscillating weight

例句：

1. 1. The floor is flat and easy to clean.
   地板是平坦的，容易清洁。
2. 2. The table is flat and perfect for a presentation.
   桌子是平坦的，非常适合做演示。
3. 3. The car was flat broke when it broke down.
   汽车抛锚时，它非常贫穷。