Please use（）for（）.

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

The vessel has stayed in port for seven days because she needs（）.

On-scene communications will normally take place between（）.

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

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

By using（）system a ship can send a distress message and know with certainty it will be received.

We consider（）send a helicopter with medical facilities to the distress area.

Radio beacon can be activated（）in case of distress.

The advantage of geostationary satellites is（）.