A.has been used
B.have been used
C.has used
D.have used
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A.have
B.had
C.are having
D.have had
A.repairs
B.repairing
C.repaired
D.being repaired
A.which is assisted
B.that assist you
C.when you assisted
D.when being assisting
A.the range of antenna can cover everywhere in the world
B.we can know the ship’s exact position
C.that the distress alert can be located as soon as possible
D.antenna of permanent earth stations may be directed towards fixed points in the sky
A.which
B.on which
C.at which
D.in which
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Stations in the United States of America are grouped by states arranged in the alphabetical order of their（）.
Monitoring is especially important in a highly automated system which is dependent on careful（）procedure and format.
Radio communication（）for many years and helps to save tens of thousands of lives.
Every ship constructed on or after（）shall comply with all the applicable requirements of this chapter.
The frequency（）the safety message will be transmitted shall be included in DSC safety call.
Every lifeboat which is fitted with a fixed two-way（）radiotelephone apparatus with an antenna which is separately mounted shall be provided with arrangements for sitting and securing the antenna effectively in its operating position.
The vessel has stayed in port for seven days because she needs（）.
（）will form the basis for distress alerting and safety calling.
As each MSI message will have a unique identity, the printing of messages already received correctly is（）.
Before GMDSS, if the radio officer on board is serious ill,（）.