单项选择题
A.When B.Where C.how D.that
（）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 reach us.
A.If B.Whenever C.Because D.Where
Before（）, a station shall take precautions to ensure th...
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
Two vessels（）while they re sailing in Huangpu River.A.s...
单项选择题Two vessels（）while they „re sailing in Huangpu River.
A.strike B.strikes C.are striking D.struck
