卡车司机在斜坡上停车时，总是记得用轮挡固定车轮。

The truck driver always remembers to put ___chocks behind the wheels when parking on a slope.

为了防止飞机滑行，地勤人员用轮挡固定住了轮胎。

The ground crew placed ___chocks under the airplane's wheels to prevent it from rolling.