plateaus , plateaux
A plateau is a large area of high and fairly flat land.
A broad valley opened up leading to a high, flat plateau of cultivated land.
一个宽阔的山谷展现在眼前,通向一片平坦的高原耕地。
If you say that an activity or process has reached a plateau, you mean that it has reached a stage where there is no further change or development.
The US heroin market now appears to have reached a plateau.
美国的海洛因市场目前似乎已进入了一个稳定阶段。