单项选择题
A.where B.when C.after D.unless
（）it is advisable to remain on a VHF channel 8, say: “s...
单项选择题（）it is advisable to remain on a VHF channel 8, say: “stand by on VHF channel 8”.
A.That B./ C.When D.What
（）we stand away from the church bell, it takes time for...
单项选择题（）we stand away from the church bell, it takes time for the sound waves to each us.
A.If B.Whenever C.Because D.Where
Before（）,a station shall take precautions to ensure tha...
单项选择题Before（）,a station shall take precautions to ensure that its emission will not interfere with transmission already in progress.
A.transmit B.to transmitting C.transmitting D.in transmitting
