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

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单项选择题
Two vessels（）while they re sailing in Huangpu River.

A.strike
B.strikes
C.are striking
D.struck
单项选择题
（）all ships in a large sea area being alerted, an “area call” will normally be transmitted so that only those ships in the vicinity of the distress incident are alerted.

A.Avoiding
B.To be avoided
C.Avoided
D.To avoid
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