Before GMDSS, if the radio officer on board is serious ill,（）.

In case a ship is in emergency or distress in any of 4 areas, it is required to use the continuous（）alert.

International Navtex service means the coordinated broadcast and automatic reception on（）khz of maritime safety information by narrow-band direct-printing telegraphy using English language.

If the beacon is mounted at a wrong place, it may（）by sea water, chemicals, exhaust and vibrations.

Please use（）for（）.

（）by an ice-breaker, it is important to maintain a continuous listening watch on the appropriate VHF channel and to maintain a proper look-out for sound and visual signals.

Monitoring is especially important in a highly automated system which is dependent on careful（）procedure and format.

At least two two-way VHF radiotelephone apparatus shall be provided on every cargo ship of（）tons gross tonnage and upwards but less than 500 tons gross tonnage.

Radio communication（）for many years and helps to save tens of thousands of lives.

The frequency（）the safety message will be transmitted shall be included in DSC safety call.