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單項(xiàng)選擇題

（）it is advisable to remain on a VHF channel 8, say: “stand by on VHF channel 8”.

A.That
B./
C.When
D.What

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單項(xiàng)選擇題

（）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

單項(xiàng)選擇題

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