测距仪的频率范围是（）。

Large airports will have round-the-clock standby emergency services, which means （ ） .

For the type of an aircraft, “combi” means the interchangeable （ ） aircraft.

A runway or a taxiway that is closed to all operations is marked with a large （ ） at each end.

The runway-in-use is normally determined by （ ） .

The runway number is determined by the （ ） of the runway.

Viewed from the aircraft, the top of the cloud looks bright, this means that the cloud layer （ ）.

An autopilot is essentially a stabilizing system which （ ） the controls during flight.

“（ ）” is the height above the ground or water of the base of the lowest layer of cloud below 6000m covering more than half the sky.

“Indicated speed” is （ ） .

Radar works on an （ ） principle.