单项选择题
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
单项选择题 The distance between the two NAVTEX stations with the same B1 character should be not exceed（）nautical miles.
单项选择题 The NAVTEX receiver can be mounted on（）.
单项选择题 （）will normally provide sufficient information to seaward of fairway buoy or pilot station.
