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單項選擇題

The identification character of each Navtex station is regarded as（）to the messages.

A.the only preamble
B.a part of the preamble
C.the closing
D.the suspension

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單項選擇題

Exchange of answerbacks act s a confirmation that the messages（）at the destination.

A.have received
B.have been received
C.are received
D.are being received

單項選擇題

The distance between the two NAVTEX stations with the same B1 character should be not exceed（）nautical miles.

A.400
B.240
C.450
D.180