clearance

飞行员在起飞前必须获得航空管制的许可。

The pilot must get ___clearance from air traffic control before takeoff.

卡车和桥底之间的间隙只有几英寸。

There's only a few inches of ___clearance between the truck and the bridge.

工人们正在进行仓库清理，为即将到来的货物腾出空间。

Workers are doing a ___clearance in the warehouse to make space for incoming goods.