无线电导航是通过对无线电信号的某一（）的测量来测定飞机的导航几何参数。

The “four Cs” for pilots to remember during an emergency stand for （ ）.

When an A/C is no longer in distress or urgency, it should （ ）.

According to ICAO, a distress message on 121.5 Mhz should begin with （ ）.

The SSR code for an A/C in distress is （ ）.

The radio call to alert ground personnel when an A/C is having difficulty, but is in no immediate danger, is （ ）.

When ground-air communication failure occurs, controller should （ ）.

If air-ground communication failure occurs, the pilot should （ ）.

To transfer communication with an A/C to another unit, the controller should pass instructions giving （ ）.

Readback is necessary in RTF because （ ）.

A controller should pass ATC clearance to a pilot at the time （ ）.