The rim is flat and there is a rather deep well, or cavetto.

边缘是平坦的，有个相当深的底部，或称为圆底。

Various vehicles bowl along over the smooth highway.

各种车辆在平坦的高速公路驶。

The river slows on the flat bottom.

河水在平坦的河床减慢流速。

Heading away from the mountains, I soon found an easier path leading downhill to the village.

我背着山走不久, 就发条通往该村比较平坦的下山小路。